Analysis of styrene oxide-globin adducts based upon reaction with Raney nickel.

A new method has been developed for determination of styrene oxide-globin adducts. The technique takes advantage of the reaction between alkylated globin and Raney nickel, which cleaves the carbon-sulfur bond in the styrene oxide-cysteine adduct to form 1-phenylethanol (1-PE) and 2-phenylethanol (2-PE). These alcohols are then reacted with pentafluorobenzoyl chloride and analyzed by GC-ECD. The method appears useful for biological monitoring of individuals exposed to styrene and, potentially, to other chemicals or their electrophilic metabolites which can react with cysteine residues in available proteins. The detection limit of the method, which is 0.04 nmol adducts/sample, indicates that it should be possible to detect adducts in the blood of people who are occupationally exposed to at least 18 mg/m3 of styrene. Analysis of globin from human whole blood which had been modified with [14C]styrene oxide indicated that 6% of the total globin adducts were detected. The method was applied to human and rat blood which had been treated with styrene oxide in vitro and to blood from rats given a single i.p. dose of styrene in vivo. Results from these experiments indicate that 77 times more adducts were detected at a given dose from rat globin than from human globin and that only 0.015% of the styrene dose was bioavailable as styrene oxide in the blood of rats. The reaction with Raney nickel is conducted at 5 degrees C to minimize unfavorable side reactions, such as degradation of 1- and 2-PE and conversion of styrene glycol to 1- and 2-PE. The optimal amount of Raney nickel was found to be 5-6 g/g globin. Since the recovery of 1-PE was not reproducible, only 2-PE is used for quantitation.     

Plasma amino acid profiles are associated with biomarkers of breast cancer risk in premenopausal Japanese women

Objective

Recently, profiles of plasma amino acids have been utilized to detect diseases including breast cancer. However, there is a possibility that the amino acid status may be associated with the risk of breast cancer. We investigated the relationship of plasma levels of amino acids with levels of sex hormones and insulin-like growth factor (IGF)-1, which are relevant to the etiology of premenopausal breast cancer, in normal premenopausal women.

Methods

Participants were 350 Japanese women who had regular menstrual cycles less than 40-day long. Fasting plasma samples were assayed for estradiol, testosterone, dehydroepiandrosterone sulfate, sex-hormone-binding globulin (SHBG), and IGF-1. A total of 20 amino acids in plasma were quantified by liquid chromatography–mass spectrometry. Information on lifestyle and reproductive factors was obtained using a self-administered questionnaire.

Results

The plasma arginine level was significantly inversely correlated with plasma levels of total and free estradiol and IGF-1 after adjusting for age, body mass index, and phase of the menstrual cycle. Plasma leucine and tyrosine levels were significantly positively correlated with the free testosterone level. The ratio of plasma asparagine to the total amino acids was significantly positively correlated with SHBG level.

Conclusions

Plasma levels of some specific amino acids, such as arginine, leucine, tyrosine, and asparagine, were associated with the levels of sex hormones, SHBG, or IGF-1 in premenopausal women. However, the present cross-sectional study cannot provide a cause–effect relation. The implication of amino acids in the etiology of breast cancer needs to be addressed in future studies.     

Reactions of methylnitrosourea, epichlorohydrin, styrene oxide and acetoxyacetylaminofluorene with polyamino acids

Radioactive methylnitrosourea, epichlorohydrin, styrene oxide,and N-acetoxy-2-acetylaminofluorene were reacted with 14 differentpolyamino acids in vitro, to determine the relative reactivityof the functional groups in amino acids. All the carcinogensreacted preferentially with polycysteine and much less withpolyhistidine. Reaction was also noted with polylysine, polymethionineand polyargjnine, as well as with DNA. Epichlorohydrin and styreneoxide reacted also with polyserine. Methylnitrosourea and N-acetoxy-2-acetylamino-fluorenereacted relatively more with polyhistidine as compared withthe epoxides. Polycysteine, polyhistidine and polylysine weremore reactive towards styrene oxide at pH 8 than at pH 6.     

Identification of c-Src tyrosine kinase substrates in platelet-derived growth factor receptor signaling

c-Src non-receptor tyrosine kinase is an important component of the platelet-derived growth factor (PDGF) receptor signaling pathway. c-Src has been shown to mediate the mitogenic response to PDGF in fibroblasts. However, the exact components of PDGF receptor signaling pathway mediated by c-Src remain unclear. Here, we used stable isotope labeling with amino acids in cell culture (SILAC) coupled with mass spectrometry to identify Src-family kinase substrates involved in PDGF signaling. Using SILAC, we were able to detect changes in tyrosine phosphorylation patterns of 43 potential c-Src kinase substrates in PDGF receptor signaling. This included 23 known c-Src kinase substrates, of which 16 proteins have known roles in PDGF signaling while the remaining 7 proteins have not previously been implicated in PDGF receptor signaling. Importantly, our analysis also led to identification of 20 novel Src-family kinase substrates, of which 5 proteins were previously reported as PDGF receptor signaling pathway intermediates while the remaining 15 proteins represent novel signaling intermediates in PDGF receptor signaling. In validation experiments, we demonstrated that PDGF indeed induced the phosphorylation of a subset of candidate Src-family kinase substrates – Calpain 2, Eps15 and Trim28 – in a c-Src-dependent fashion.     

Isolation and characterization of two benzene-derived hemoglobin adducts in vivo in rats.

The present study was aimed at the characterization of the major adducts formed by reaction of the metabolites of [14C]benzene with rat hemoglobin in vivo. Groups of 12-week-old male Fisher rats received i.p. injections of a single dose of 10 mmol/kg body weight or three equal daily subdoses of 3.3 mmol/kg body weight of [14C]benzene. High-performance liquid chromatographic analysis of strong acid hydrolysates of the [14C]benzene-modified globin indicated that the two major adducts in rats cochromatographed with synthetic S-(2,5-dihydroxyphenyl)cysteine and S-phenylcysteine. These adducts were converted to O,O'-S-tris-acetyl-3-thiol-hydroquinone and S-phenylthioacetate, which were then characterized by gas chromatography/mass spectrometry. The major radioactive adduct peaks accounted for 60-75% of the total radioactivity associated with rat globin. Characterization of the S-(2,5-dihydroxyphenyl)cysteine adduct provides evidence that p-benzoquinone is formed as a reactive metabolite of benzene. Formation of the S-phenylcysteine adduct indicates that benzene oxide and/or a hydroxycyclohexadienyl free radical is formed as an active intermediate upon i.p. injection of benzene into rats.     

Expression of carcinoembryonic antigen and its predicted immunoglobulin-like domains in HeLa cells for epitope analysis.

Carcinoembryonic antigen (CEA) is a member of the immunoglobulin gene superfamily with one predicted variable domain-like region (N domain; 108 amino acids) and three sets of constant domain-like regions (A1B1, A2B2, and A3B3; 92 amino acids for A domains and 86 amino acids for B domains). In addition, CEA possesses two signal peptides, one at the amino terminus and one at the carboxyl terminus. Both are removed during posttranslational processing, with the one at the carboxyl terminus being replaced by a glycosylphosphatidylinositol (GPI) moiety. We have previously expressed the full length complementary DNA clone for CEA in Chinese hamster ovary cells and murine L cells, demonstrating proper processing of nascent polypeptide chains to mature, fully glycosylated CEA including the GPI anchor. Using the same full length CEA complementary DNA clone and the polymerase chain reaction, we have now constructed expression clones for secreted versions of the N domain, the A3B3 domain, and the A3 and B3 subdomains. The clones were expressed in HeLa cells using the beta-actin promoter. A stop codon was introduced at the end of the A3B3 and the A3 and B3 domains to allow secretion instead of retention on plasma membranes with the GPI anchor. Expressed products were purified to homogeneity by affinity chromatography using monoclonal antibodies specific for each domain and by reversed phase high pressure liquid chromatography. Purified domains were characterized by Western blotting, antibody binding and inhibition studies, amino-terminal sequence and amino acid analyses, and laser desorption/time of flight mass spectrometry. These analyses revealed that the monomeric N domain is of size 15,990, with a glycosylation mass of about 4100, in good agreement with two N-linked glycosyl units of about mass 2100. There is some evidence that the N domain forms dimers. The N domain reacted with antibodies specific for this domain with an affinity similar to that of intact CEA. The A3B3 domain had a mass of 34,462, with a glycosylation mass of 14,900, in good agreement with seven N-linked glycosylation sites of average mass 2100. The A3B3 domain reacted only with antibodies specific for this domain, with a slightly lower affinity than that of native CEA. The amino-terminal sequences of the N domain and A3B3 domain proteins demonstrated proper processing of the signal peptide.(ABSTRACT TRUNCATED AT 400 WORDS)     

The proto-oncogene c-ros codes for a transmembrane tyrosine protein kinase sharing sequence and structural homology with sevenless protein of Drosophila melanogaster

Our earlier study predicted that proto-oncogene c-ros codes for a receptor-like tyrosine protein kinase (TPK). To further understand its protein structure and physiological function, we have analysed its expression in various tissues of chicken and have isolated and sequenced cDNA clones containing the entire coding region of the gene. Confirming our earlier study, we found that kidney is the organ that expresses the highest level of c-ros mRNA, in addition, we found a lower level of expression in gonad, thymus, bursa and brain. A distinctive 8.3 kb c-ros mRNA is present in kidney. No detectable amount of c-ros mRNA was found in the rest of tissues examined. Nucleotide sequence of the c-ros cDNA predicts that it codes for a transmembrane (TM) TPK molecule of 2311 amino acids (aa). The extracellular domain consists of 1873 amino acids which share 20 to 43% homology with that of the Drosophila sevenless protein and TPK domains of the two genes have 58 to 74% homology. The extracellular domain containing 37 potential N-linked glycosylation sites is preceded by a 5' hydrophobic sequence resembling a typical signal peptide. An internal hydrophobic domain of 26 amino acids, the presumed transmembrane domain, is followed by a spacer sequence of 58 amino acids, a TPK domain of 270 amino acids and a carboxyl tail of 84 amino acids. Overall, our result indicates that c-ros codes for a glycosylated transmembrane TPK molecule which shares a remarkable sequence and structural homology with that of Drosophila sevenless protein.     

Binding of [3H]benzo(a)pyrene to natural and synthetic nucleic acids in a subcellular microsomal system.

Several carcinogens are bound covalently to cellular nucleic acids. This is also the case with polycyclic hydrocarbon carcinogens, but their precise mechanism of in vivo activation to reactive forms and the structure(s) of the nucleic acid adducts are not known. This study demonstrates that in the presence of rat liver microsomes and reduced nicotinamide adenine dinucleotide phosphate there is covalent attachment of tritiated benzo(a)pyrene (BP) to transfer RNA, DNA, certain synthetic polyribonucleotides, and an RNA species endogenous to the microsomal fraction. Evidence has been obtained that the binding occurs mainly to guanine and, to a lesser extent, adenine residues and is not simple an artifact of tritium exchange. The microsomal-mediated binding of [3H]BP to nucleic acids requires reduced nicotinamide adenine dinucleotide phosphate and in inhibited by 7,8-benzoflavone, glutathione, and magnesium. It is enhanced somewhat by the addition of styrene oxide, cyclohexene oxide, and trichloropropylene oxide. These results provide the first evidence that: (a) the microsome-mediated binding of [3H]BP to nucleic acids is not just due to tritium exchange; (b) a derivative of the hydrocarbon is covalently bound to the nucleic acid, and not simply intercalated; (c) there is a preferential binding to guanine residues; and (d) in addition to binding to exogenous nucleic acids, [3H]BP is bound to an RNA species present in the microsomes. Our data are consistent with but do not prove that nucleic acid binding of this polycyclic hydrocarbon proceeds via an epoxide intermediate.     

Molecular dosimetry of polycyclic aromatic hydrocarbon epoxides and diol epoxides via hemoglobin adducts

Ten reactive metabolites of five polycyclic aromatic hydrocarbons and styrene were investigated to determine the generality of ester adduct formation with human hemoglobin in the form of RBC and hydrolysis to the corresponding tetrahydrotetrols or dihydrodiols. No exceptions were noted among the compounds tested, which included the anti-diol epoxides of benzo[a]pyrene (BaP), chrysene, and benz[a]anthracene; the syn-diol epoxide of BaP; a mixture of syn- and anti-diol epoxides of benzo[e]pyrene; and epoxides of styrene, benzo[e]pyrene, BaP, and cyclopenta[c,d]pyrene. A test of the propensity of the simplest benzylic epoxide, styrene oxide, to form esters that hydrolyze via a BAL1 mechanism was performed. Hydrolysis of styrene oxide-adducted hemoglobin in H2(18)O at neutral pH yielded 18O incorporation results that suggest this mechanism of hydrolysis is operant to a minor degree in styrene oxide-hemoglobin ester adducts. A method was developed for the isolation and quantification of the polycyclic aromatic alcohols, which consists of enzymatic proteolysis, immunoaffinity chromatography, and gas chromatography-mass spectrometry or fluorimetry. The method allows for routine analysis of hemoglobin from individual samples as small as 1 ml of whole blood. Analysis of blood from different human populations revealed that hemoglobin adducts of the anti-diol epoxide of BaP dominated the spectrum of adducts formed by the selected metabolites.     

Structural characterization by mass spectrometry of hemoglobin adducts formed after in vitro exposure to methyl bromide

A mass spectrometric procedure is described for the structuralstudy of the adducts formed in human hemoglobin by in vitroexposure of erythrocytes to the alkylating agent methyl bromideusing different protein to reagent ratios. Peptide mapping byHPLC and tandem mass spectrometry allowed location of methylatedamino acids within the protein sequence. A prominent reactivityof several nucleo-philic side chains in human hemoglobin summitswas observed, which was modulated by the concentration of thealkylating agent Cysteine residues, the main reactive sites,were fully methylated in hemoglobin exposed to a 10-fold excessof methyl bromide, differently from other residues, includinghistidines, showing a heterogeneous pattern of methylation thatwas largely directed by their environment. No evidence of methylationwas found at the heme proximal histidines ß92 and     

In-vitro assays to detect alkylating and mutagenic activities of dietary components nitrosated in situ

Nitrosation of dietary components has been combined with the 4-(para-nitrobenzyl)pyridine (NBP) colorimetric test for screening alkylating agents and with the Ames test for the detection of mutagenic activity. This allowed the investigation of short-lived nitrosation products of dietary components which generate electrophilic degradation products requiring no metabolic activation (natural amino acids and some derivatives, ureas, guanidines, primary alkyl and aryl amines). In a first system, precursor, nitrous acid and NBP were present simultaneously. All amino acids tested, except glutamic acid and glutamine, gave positive results. The reactivities spanned more than three orders of magnitude, with the aromatic amino acids and methionine the most active; two primary amines, tryptamine and histamine, were also strongly reactive. All guanidines tested, except the amino acid arginine, gave negative results. A second system consisted of two phases: NBP was added only after destruction of residual nitrite and adjustment of the pH to neutrality. This system was useful for the study of ureas, which are stable in acid but not in neutral media. The range of responses covered more than two orders of magnitude. Most amino acids and primary amines also gave positive results, but could be assessed only after analysing the kinetics of the competing reactions and choosing appropriate reaction times. In a third system, Salmonella typhimurium strain TA100 replaced NBP. Representatives of the class of amino acids, ureas, the primary amine tryptamine, and aniline became highly mutagenic upon nitrosation. Methylguanidine was only weakly mutagenic under the present assay conditions. The results indicate that further studies with unstable nitrosation products of dietary components are required to understand more thoroughly the role of endogenous nitrosation in gastric cancer.     

Analysis of the binding sites of chromium to DNA and protein in vitro and in intact cells.

Previous studies have examined Cr(III), or CrO4 reduced to Cr(III), binding in vitro to DNA. However, there have been few studies examining chromate binding to DNA in intact cells. Treatment of intact cells with chromate (Na2(51)CrO4) resulted in chromium (Cr) binding to DNA. The binding of Cr to DNA was much more stable when more residual peptide/amino acids were associated with DNA. A substantial portion of the Cr bound to DNA was released by treatment with EDTA, suggesting that trivalent Cr was the major oxidation state of Cr bound to DNA. Cr(III) stimulated the formation of amino acid-DNA and protein-DNA complexes in vitro. Tyrosine and cysteine exhibited the highest activity in being complexed to DNA by Cr(III) in vitro, while histidine, methionine and threonine also exhibited more activity than any other amino acid. Similar results were found in intact cells. The activity of proteins complexed to DNA by trivalent Cr depended upon the content of these reactive amino acids. Thus, bovine serum albumin was more active than actin, which in turn was more active than histones. These and other studies presented suggested that Cr(III) was involved directly in the formation of DNA-protein complexes in intact cells, unlike other metals such as Ni(II), which are thought to form DNA-protein cross-links catalytically and not participate directly in the complex. The majority of trivalent Cr associated with DNA was bound to the phosphate backbone without exhibiting any base specificity. Collectively, these results indicate that trivalent Cr creates DNA protein crosslinks by binding with reactive amino acids (i.e. cysteine, tyrosine or histidine) and linking these to the phosphate backbone of DNA.     

Radiochemical investigations of gastrin-releasing peptide receptor-specific [(99m)Tc(X)(CO)3-Dpr-Ser-Ser-Ser-Gln-Trp-Ala-Val-Gly-His-Leu-Met-(NH2)] in PC-3, tumor-bearing,rodent models: syntheses,radiolabeling, and in vitro/in vivo studies where Dpr = 2,3-diaminopropionic acid and X = H2O or P(CH2OH)3

Bombesin (BBN), a 14 amino acid peptide, is an analogue of human gastrin-releasing peptide (GRP) that binds to GRP receptors (GRPrs) with high affinity and specificity. The GRPr is overexpressed on a variety of human cancer cells, including prostate, breast, lung, and pancreatic cancers. The specific aim of this study was to develop (99m)Tc(I)-radiolabled BBN analogues that maintain high specificity for the GRPr in vivo. A preselected synthetic sequence via solid phase peptide synthesis was designed to produce 2,3-diaminopropionic acid (Dpr)-BBN conjugates with the following general structure: Dpr-Ser-Ser-Ser-Gln-Trp-Ala-Val-Gly-His-Leu-Met-(NH(2)). The new BBN constructs were purified by reversed phase high-performance liquid chromatography. Electrospray mass spectrometry was used to characterize the nonmetallated BBN conjugates. Re(I)-BBN conjugates were prepared by the reaction of [Re(Br)(3)(CO)(3)](2-) and Dpr-Ser-Ser-Ser-Gln-Trp-Ala-Val-Gly-His-Leu-Met-(NH(2)) with gentle heating. Electrospray mass spectrometry was used to determine the molecular constitution of the new Re(I) conjugates. The (99m)Tc conjugates were prepared at the tracer level by preconjugation, postlabeling approach from the reaction of [(99m)Tc(H(2)O)(3)(CO)(3)](+) and corresponding ligand. The (99m)Tc and Re(I) conjugates behaved similarly under identical reversed phase high-performance liquid chromatography conditions. Results from in vitro and in vivo models demonstrated the ability of these derivatives to specifically target GRPrs on human, prostate, cancerous PC-3 cells.     

Differential requirement of the last C-terminal tail of Met receptor for cell transformation and invasiveness

Biological responses to Hepatocyte Growth Factor are mediated by the tyrosine kinase receptor encoded by the Met oncogene. Under physiological conditions, Met triggers a multi-step genetic program called 'invasive growth' including cell-dissociation, invasion of extracellular matrices and growth. When constitutively activated, Met can induce cell transformation and metastasis. Phosphorylation of two docking tyrosines in the receptor tail is essential for all biological responses. To investigate the role of the C-terminal part of Met, we have generated mutants lacking either the last 26 or 47 amino acids. As expected, mutants lacking the docking sites fail to mediate cell transformation and invasion. Interestingly, while Met Delta26 can mediate invasion, its transforming ability is severely impaired. Moreover, the lack of the last 26 amino acids strongly reduces Met ability to phosphorylate substrates in vitro and in vivo. These data indicate that the last 26 amino acids are required to confer the kinase its full enzymatic activity, which is critical for cell transformation but dispensable for invasive properties. Finally, we also show that up-regulation of Met enzymatic activity by insertion of a point mutation in the kinase domain (M1250T) overcomes the regulatory role played by the last 26 amino acids of the tail. It is concluded that the C-terminal domain of Met is crucial not only for recruitment of transducers but also for regulation of receptor enzymatic activity.     

Amino acid profile index for early detection of endometrial cancer: verification as a novel diagnostic marker

Background

Plasma amino acid profiles (PAAPs) vary in individual cancer patients, and it has been suggested that they may be useful for early detection of several types of cancer. We evaluated the diagnostic performance of a profile index for endometrial cancer composed of multiple plasma amino acids as a novel biomarker and compared its diagnostic performance with that of CA125.

Methods

Plasma amino acid levels of 80 patients with endometrial cancer, 122 with benign gynecological diseases, and 240 age- and body mass index-matched control subjects were measured using liquid chromatography and mass spectrometry. After univariate analysis, we applied a multiplex model based on the PAAP multivariate analysis to distinguish patients with endometrial cancer from control subjects. We compared the diagnostic performance of the multiple PAAP index (API) with that of CA125.

Results

The levels of several plasma amino acids were significantly different in patients with endometrial cancer. The area under the receiver operating characteristic curves (AUC) used to distinguish endometrial cancer patients from control subjects was 0.94. The AUC for API was significantly larger than that for CA125 (P = 0.0068). For the same specificity of 98.3 %, API showed a significantly higher sensitivity (60.0 %, 95 % CI, 43.3–75.1) than that of CA125 (22.5 %, 95 % CI, 10.1–38.5). In stage I cases, API showed significantly higher positivity than that of CA125 (P = 0.0002).

Conclusions

The sensitivity and disease specificity of API for early-stage detection of endometrial cancer was superior to CA125. This novel plasma biomarker has the potential to become a diagnostic and screening marker for endometrial cancer.     

Alkylating potency of nitrosated amino acids and peptides.

The alkylating potency of unstable N-nitrosamino acids and N-nitrosopeptides was investigated in vitro using 4-(para-nitrobenzyl)pyridine (NBP) as nucleophile. Of the amino acids, Met and those with an aromatic side chain were the most potent. The relative overall alkylating potency was 23:10:5:4:2:1: for Trp, Met, His, Tyr, Phe and Gly, respectively. The homo-dipeptides were much more potent than the amino acids, with relative potencies of 400:110:100:8:3:1, for Trp-Trp, Tyr-Tyr, Met-Met, Asp-Asp, Phe-Phe and Gly, respectively. In the one-phase reaction system (in which NBP is already present during the nitrosation reaction at acidic pH), all amino acids tested showed a second-order reaction for nitrite. In the two-phase system (in which NBP is added only after bringing the nitrosation reaction mixture to neutrality), all amino acids tested except one again showed a second-order reaction for nitrite (Phe, His, Asp and the dipeptide artificial sweetener aspartame); only Met under these conditions had a reaction order of one for nitrite. This could mean that nitrosation of the side chain of Met produces a second N-nitroso product which is relatively stable in acid but reacts with NBP under neutral conditions. In the human stomach, this side-chain nitrosation might become more important than the reactions at the primary amino group, firstly because of the greater stability of the product(s) in acid and secondly because of the first-order reaction rate for nitrite.(ABSTRACT TRUNCATED AT 250 WORDS)     

Detection of DNA adducts by postlabelling with 3H-acetic anhydride

A method has been developed for detecting 7-alkylguanines which is based on derivatization of hydroxyl and primary amino groups with 3H-acetic anhydride. The derivatization procedure is devised for 7-methylguanine, with examination of reaction kinetics. The method is applied to the detection of the isomeric styrene oxide-guanine adducts; styrene-7,8-oxide is the active metabolite of styrene. The procedure can be used as a postlabelling method for the simultaneous detection of several adducts after selective depurination of 7-alkylguanines from DNA.     

Low postabsorptive net protein degradation in male cancer patients: lack of sensitivity to regulatory amino acids?

Autophagic (lysosomal) and proteasomic protein degradation are important regulatory mechanisms in the homeostasis of muscle mass, that may be profoundly disturbed in cancer and other wasting syndromes. Due to the inhibiting effect of amino acids and insulin, net proteolysis is restricted to the fasted state, and in autophagy certain amino acids have been identified as 'regulatory' in the rat, including leucine, tyrosine, phenylalanine, methionine, and histidine (i.e. LYFMH). The present cross-sectional study assessed postabsorptive net protein catabolism in male cancer patients as well as in healthy male volunteers, to analyse its relation to such 'regulatory amino acids'. Postabsorptive amino acid exchange rates across the leg were determined in patients with gastrointestinal cancer (GIC, n=47) or renal cell carcinoma (RCC, n=15), age-matched (n=33), and young male control subjects (n=42). Both groups of cancer patients revealed a significantly lower postabsorptive net protein catabolism than control subjects. Furthermore, in the control subjects, the postabsorptive net protein catabolism was found to be inversely and significantly correlated with the arterial concentrations of the 8 amino acids YSHMFGI and L which include 5 of the 'regulatory amino acids'. Cancer patients, in contrast, revealed no such significant correlations. These results may indicate i) that postabsorptive net protein catabolism in skeletal muscle of healthy subjects may be sensitive to amino acids which reportedly regulate autophagy and ii) that such amino acid-sensitive mechanism of protein catabolism may be disturbed in cancer patients.     

Irradiation-induced adduct formation of RNA with carcinogenic arylamine derivatives.

Radiolysis of N2O-saturated solutions of transfer RNA (tRNA) and the arylacethydroxamic acids, N-hydroxy-N-2-acetylaminofluorene and N-hydroxy-N-4-acetylaminobiphenyl; their corresponding acetamides, 2-acetylaminofluorene and 4-acetylaminofluorene; or the O-glucuronide of N-hydroxy-N-2-acetylaminofluorene resulted in adduct formation of the nucleic acid with these carcinogenic arylamine derivatives. The yield of adducts on irradiation of the arylacethdroxamic acids with tRNA was greater than that for their corresponding acetamides or the O-glucuronide. The fluorenylacethydroxamic acid and acetamide were also more reactive than the biphenyl analogs. Adduct formation resulting from radiolysis of tRNA and the arylacethydroxamic acids or the O-glucuronide proceeded with retention of both the aromatic nucleus and the N-acetyl group. The yields of adducts were much greater for irradiated mixtures than for irradiation of either component alone followed by mixing. Evaluation of the data shows that initial modification of the tRNA or the carcinogen can lead to adduct formation. In the case of primary radical attack of the nucleic acid, it has been shown that short-lived reactive RNA intermediates are responsible for a major fraction of the observed yield of adducts in the irradiated mixtures. Comparative studies showed that irradiation under conditions that favor reaction of oxidizing radicals enhanced formation of the adducts. Oxygen was shown to protect RNA from irradiation-induced binding of the arylacethydroxamine acids due to competition of O2 with the carcinogen for the reactive RNA intermediates.     

Characterization of phosphodiester adducts produced by the reaction of cyanoethylene oxide with nucleotides

Cyanoethylene oxide (CEO), a putative toxic and carcinogenicmetabolite of acrylonitrile, is a direct-acting mutagen. Thefocus of this study was to elucidate potential adducts responsiblefor the mutagenic effect of CEO by characterizing products fromthe reaction of CEO with nucleotides. The reaction of CEO withthe 5'-monophosphates of deoxy-guanosine, deoxyadenosine, deoxycytidineor deoxythymidine resulted in the formation of at least oneadduct for each nucleotide. Using two-dimensional NMR spectroscopyand fast atom bombardment mass spectrometry, CEO-nucleotideadducts (