INVOLVEMENT OF GENETIC POLYMORPHISM OF ALCOHOL AND ALDEHYDE DEHYDROGENASES IN INDIVIDUAL VARIATION OF ALCOHOL METABOLISM

The involvement of genetic polymorphism at the alcohol dehydrogenase2 (ADH2) and aldehyde dehydrogenase 2 (ALDH2) loci in determiningblood acetaldehyde levels and the rate of ethanol eliminationafter ethanol intake was investigated. Sixty-eight healthy subjectsingested 0.4 g of ethanol per kg of body weight over 10 min.Blood acetaldehyde levels scarcely increased in the subjectshomozygous for ALDH2^*I, regardless of their ADH2 genotypes (ADH2^*1/^*1,ADH2^*1/^*2 and ADH2^*2/^*2). The acetaldehyde levels in the subjectswith the ALDH2^*1/^*2 heterozygote increased to 23.4 µMon average, and no significant differences were observed betweenthe three ADH2 genotype groups. Subjects homozygous for ALDH2^*2showed very high levels of blood acetaldehyde, and the averagevalue was 79.3 µM. The values of Widmark's ß₆₀(mg/ml/hr)and ethanol elimination rate (mg/kg/br) showed significant differencesamong the three ALDH2 genotypes, and in decreasing order thevalues were ALDH2^*1/^*1, ALDH2^*1/^*2, ALDH2^*2 However, no significantdifferences were seen among the ADH2 genotypes.     

PHOSPHORYLATION OF CYTOCHROME P4502E1 (CYP2E1) BY CALMODULIN DEPENDENT PROTEIN KINASE PROTEIN KINASE C AND cAMP DEPENDENT PROTEIN KINASE

Phosphorylation of pure cytochrome P4502E1 (CYP2E1) was achievedin vitro using Ca²⁺/calmodulin-dependent protein kinase II (CaMkinase II), protein kinase C (PKC) and cAMP-dependent proteinkinase (PKA). The stoichiometry and time-course of phosphorylationwere determined. CaM kinase II was the most efficient enzymecapable of catalyzing this phosphorylation reaction: the maximumincorporation of ³²PO₄ was 0.8 mol/mol CYP2E1 in 20 min. PKAphosphorylated a maximum of 0.7 mol of ³²PO₄/ mol of cytochromewithin 60 min. The phosphorylation by PKC reached a maximumof 0.19 mol of ³²PO₄/mol of cytochrome and this occurred withina few minutes of incubation. Limited digestion by S. aureusV8 protease (SAP) of CYP2E1, which had been phosphorylated byeither PKA and PKC, yielded a single major phosphopeptide withan M_r of approximately 18,000. Limited digestion of CYP2E1,that had been phosphorylated by CaM kinase II, yielded phosphorylatedpolypeptides with M_r of approximately 18,000 and 15,000. Theseresults raise the possibility that these three kinases may beinvolved in the regulation of CYP2E1.     

Distribution of ADH1B, ALDH2, CYP2E1∗6, and CYP2E1∗7B genotypes in Turkish population

The most well-known metabolic pathways from ethanol to acetaldehyde include alcohol dehydrogenase (ADH) and the microsomal ethanol oxidizing system that involves cytochrome P450 2E1 (CYP2E1). Acetaldehyde is further oxidized to acetate by aldehyde dehydrogenase (ALDH). The genetic variation of ADH1B, ALDH2, and CYP2E1 is different among racial populations and cause difference in elimination rates of alcohol. The aim of this study was to determine the polymorphisms of ADH1B (rs1229984; Arg47His), ALDH2 (rs671; Glu487Lys), CYP2E1*6 (rs6413432; T7632A), and CYP2E1*7B (rs6413420; G-71T) in unrelated healthy Turkish population and compare it with other populations. ADH1B and ALDH2 polymorphisms were analyzed with an allele-specific polymerase chain reaction (PCR) assay, and CYP2E1*6 and CYP2E1*7B polymorphisms were genotyped by PCR-restriction fragment length polymorphism method. ADH1B polymorphism analysis yielded the genotype distribution as 83.9% ADH1B*1/1 and 16.1% ADH1B*1/2, and no individuals with ALDH2*1/2 and ALDH2*2/2 genotypes were found in Turkish population. The genotype frequencies for CYP2E1*6 polymorphism were found as 85.3% for homozygote common, 14.1% for heterozygote, and 0.6% for homozygote uncommon. For CYP2E1*7B polymorphism, the genotype frequencies were determined to be 86.5% G/G, 13.5% for G/T; however, no individuals with homozygote uncommon genotype were detected. According to our study results, the genotype distributions of ADH1B, ALDH2, CYP2E1*6, and CYP2E1*7B in Turkish population were similar compared with Caucasian and some European populations, whereas differed significantly from East Asian populations. This study may be useful in epidemiological studies of the influence of ADH1B, ALDH2, CYP2E1*6, and CYP2E1*7B polymorphisms on diseases, including several types of cancer related to alcohol consumption and alcohol dependence.     

CHARACTERISTICS OF ALDEHYDE DEHYDROGENASES OF CERTAIN AEROBIC BACTERIA REPRESENTING HUMAN COLONIC FLORA

We have proposed the existence of a bacteriocolonic pathwayfor ethanol oxidation resulting in high intracolonic levelsof toxic and carcinogenic acetaldehyde. This study was aimedat determining the ability of the aldehyde dehydrogenases (ALDH)of aerobic bacteria representing human colonic flora to metabolizeintracolonically derived acetaldehyde. The apparent Michaelisconstant (K_m) values for acetaldehyde were determined in crudeextracts of five aerobic bacterial strains, alcohol dehydrogenase(ADH) and ALDH activities of these bacteria at conditions prevailingin the human large intestine after moderate drinking were thencompared. The effect of cyanamide, a potent inhibitor of mammalianALDH, on bacterial ALDH activity was also studied. The apparentK_m for acetaldehyde varied from 6.8 (NADP⁺ -linked ALDH of Escherichiacoli IH 13369) to 205 µM (NAD⁺ -linked ALDH of Pseudomonasaeruginosa IH 35342), and maximal velocity varied from 6 nmol/min/mg(NAD⁺ -linked ALDH of Klebsiella pneumoniae IH 35385) to 39nmol/min/mg (NAD⁺ -linked ALDH of Pseudomonas aeruginosa IH35342). At pH 7.4, and at ethanol and acetaldehyde concentrationsthat may be prevalent in the human colon after moderate drinking,ADH activity in four out of five bacterial strains were 10–50times higher than their ALDH activity. Cyanamide inhibited onlyNAD⁺ -linked ALDH activity of Pseudomonas aeruginosa IH 35342at concentrations starting from 0.1 mM. We conclude that ALDHsof the colonic aerobic bacteria are able to metabolize endogenicacetaldehyde. However, the ability of ALDHs to metabolize intracolonicacetaldehyde levels associated with alcohol drinking is ratherlow. Large differences between ADH and ALDH activities of thebacteria found in this study may contribute to the accumulationof acetaldehyde in the large intestine after moderate drinking.ALDH activities of colonic bacteria were poorly inhibited bycyanamide. This study supports the crucial role of intestinalbacteria in the accumulation of intracolonic acetaldehyde afterdrinking alcohol. Individual variations in human colonic floramay contribute to the risk of alcohol-related gastrointestinalmorbidity.     

GENETIC POLYMORPHISMS OF ALCOHOL METABOLIZING ENZYMES RELATED TO ALCOHOL SENSITIVITY AND ALCOHOLIC DISEASES

Indiciduals with the atypical aldehyde dehydrogenase ALDH₂²allele, both homozygous and heterozygous status, are alcoholsensitive and have a markedly reduced risk of developing alcoholicdiseases. Genetic abnormalities of the ALDH₁ locus are alsoassociated with alcohol flushing. The ALDH₃ and ALDH_x, lociare polymorphic and their variations may affect the developmentof alcoholic diseases. The variations of alcohol dehydrogenaseADH₂ and ADH₃ loci have no profound effects on alcohol sensitivity.The newly identified ADH₆ gene has hormone response elements,and it may cause the gender difference in alcoholic problems.     

ALCOHOL DEHYDROGENASE POLYMORPHISMS IN NATIVE AMERICANS: IDENTIFICATION OF THE ADH2*3 ALLELE

Alcohol dehydrogenase (ADH) polymorphisms were evaluated among95 Native American Mission Indians. Approximately equal frequenciesof ADH3^*1 and ADH3^*2 alleles were found. Twelve individualswere heterozygous for ADH2^*3, an allele previously identifiedonly in persons of African origin. None of the individuals withADH2^*3 alleles was of purely Native American descent, althoughnone had known African ancestry. These results suggest thatthese candidate genes deserve broader study among Native Americansand may provide increased understanding of the likely polygeniccontributions to alcohol-related disorders in this population.     

The A1 allele of the D2 dopamine receptor gene is associated with high dopamine transporter density in detoxified alcoholics

The A1 allele of TaqI A restriction fragment length polymorphism(RFLP) in the D₂ receptor (DRD₂) gene locus has been suggestedto be associated with low D₂ receptor density in man. Striataldopamine transporter (DAT) densities were studied with [¹²³I]2-ß-carbometoxy-3ß(4-iodophenyl)tropaneand single-photon emission tomography in 29 detoxified alcoholics,who were also genotyped for the two alleles of TaqI A RFLP atthe DRD2 receptor gene locus. Alcoholics with the A1/A2 genotypes(n = 10) had statistically significantly higher DAT densitiesthan subjects with the A2/A2 genotypes [n = 19; 8.0 ±1.2 (mean ± SD) vs 6.9 ± 1.1, P = 0.035]. We suggestthat the TaqI A RFLP is in linkage disequilibrium with a genevariant modifying DAT density in alcoholics.     

ALTERATION OF ACETALDEHYDE METABOLISM IN CARBON TETRACHLORIDE-INTOXICATED RAT LIVER: ANALYSIS USING LIVER PERFUSION SYSTEM

The hepatic metabolism of acetaldehyde in carbon tetrachloride(CCl₄)-intoxicated rats was studied using a non-recirculatinghaemoglobin-free liver-perfusion system. Acetaldehyde uptakeby the liver from acutely CCl₄-treated animals (4.16 mmol/kg,i.p.) at 24 hr after the treatment was not significantly altered,whereas that by the liver from chronically CCl₄-treated animals(2.08 mmol/kg,i.p., twice a week, for 8–12 weeks) wasdecreased by approximately 50% when it was determined in thepresence of 0.01–5 mM acetaldehyde. In liver from ratschronically intoxicated with CCl₄, the following important biochemicalchanges were observed: (1) The activity of low K_m aldehyde dehydrogenase(ALDH) in hepatic mitochondria was decreased by approximately75%. (2) The basal levels of the lactate/pyruvate (cytosolic[NADH]/[NAD⁺]) ratio as well as the ß-hydroxybutyrate/acetoacetate(mitochondrial [NADH]/[NAD⁺]) ratio were elevated by more than2-fold. (3) Mitochondrial NADH oxidation was also reduced byapproximately 35% of the control level. (4) The basal levelof hepatic oxygen uptake was attenuated by approximately 50%,and the infusion of acetaldehyde (0.01–5.0 mM) causeda further decrease in the uptake. (5) The rate of ethanol productionfrom acetaldehyde by the catalytic action of alcohol dehydrogenasewas found to be unaltered when low concentrations of acetaldehyde(0.01–0.2 mM) were used, whereas a significant suppressionof the rate of ethanol production was detected in the presenceof high concentrations of acetaldehyde (0.6–5 mM). Thesedata suggest that the changes in activity of the lowK_m mitochondrialacetaldehyde dehydrogenase and those in mitochondrial NADH oxidationcoupled with mitochondrial respiration may, at least in part,play important roles in the decreased hepatic acetaldehyde metabolismobserved in chronically CCl₄-treated rats.     

RATES OF METABOLISM OF ETHANOL TO ACETATE BY HUMAN NEUTROPHIL PRECURSORS AND MACROPHAGES

Studies employing uninduced and dimethylsulphoxide-induced HL60)cells have shown that (1) promyelocytes metabolise ethanol (0.1mg/ml) to acetate at the rate of 3.9 nmol/10⁷ cell/hr and (2)there is a progressive fall in the ethanol-metabolislng capacityas promyelocytes mature into neutrophil myelocytes and, eventually,to band forms and neutrophil granulocytes. By contrast, macrophagesderived from the treatment of HL60 cells with 1,25 [OH]₂ vitaminD₃ and from the culture of normal blood monocytes metabolisedethanol to acetate at much higher average rates of 180.1 and184.7 nmol/10⁷ cell/hr. Furthermore. nucleated marrow cell suspensionswhich were depleted of cells capable of adhering to plasticmetabolised ethanol at only one-third the rate shown by non-depletedcell suspensions. The data indicate that neutrophils and theirgranule-contaming precursors contribute relatwely little andmacrophages contribute substantially to the overall rate ofethanol metabolism by suspensions of nucleated marrow cells.In addition, the considerable capacity of macrophages to mctaboliscethanol in vitro raises the possibility that the metabolismof ethanol by thew cells in vivo may result in some deleteriouseffect on surrounding cells and thus. account, at least in part.for ethanol-induced tissue damagealcoholic subjects is reported.Further studies are needed to confirm this latter finding andto assess fully its possible significance.     

ETHANOL AND PHOSPHATIDYLETHANOL REDUCE THE BINDING OF [3H]INOSITOL 1,4,5-TRISPHOSPHATE TO RAT CEREBELLAR MEMBRANES

In this study, we have analysed the effect of ethanol and phosphatidylethanol,a unique phospholipid formed only in the presence of ethanol,on the binding of [³H]inositol 1,4,5-trisphosphate to rat cerebellarmembranes. Rats were intraperitoneally injected daily with 3g of ethanol/kg body weight for different periods of time. Repeatedadministration of ethanol induced a reduction in the bindingcapacity (B_max) without affecting the affinity constant (K_d).A significant 32% reduction was observed after 21 days of exposure(from control B_max values of 25±3 pmol/mg and K_d valuesof 9±2 nM). In an in-vitro assay, phosphatidylethanol(500 µM) and phosphatidic acid (500 µM), but noother phospholipids tested, induced a reduction in B_max (39%and 43%, respectively). The observed effect displayed by phosphatidylethanolwas not due to its degradation to phosphatidic acid or otherphospholipids. The results emphasize the importance of examiningphosphatidylethanol (PEth) as a possible mediator of the effectsof ethanol on cellular processes. However, the role of PEthin the observed effect of long-term ethanol exposure still needsfurther consideration.     

D2 DOPAMINE RECEPTOR TaqI ALLELES IN MEDICALLY ILL ALCOHOLIC AND NONALCOHOLIC PATIENTS

The prevalence of TaqI A alleles of the D₂ dopamine receptor(DRD2) gene was examined in two subgroups of medically ill nonalcoholics(more prevalent and less prevalent substance users, MPSU andLPSU, respectively) and in two subgroups of medically ill alcoholics(more severe and less severe alcoholics, MSA and LSA, respectively).The prevalence of the Al allele in the 80 nonalcoholic and 73alcoholic patients was 30.0% and 52.1%, respectively (P = 0.009).In the four subgroups of these patients, the prevalence of thisallele was: LPSU = 18.2%, MPSU = 34.5%, LSA = 44.4% and MSA= 58.3%. Linear trend analysis showed that as the use of substancesand severity of alcoholism increase, so does Al prevalence (P= 0.001). Specific, subgroup comparisons showed Al prevalencein MSA to be about 3-fold (P = 0.007) and 1.5-fold (P = 0.04)higher than in LPSU and MPSU subgroups, respectively. Similarly,in a combined analysis of independent studies, Al prevalencein MSA was higher when compared to LSA (P < 5 x 10^–3),MPSU (P < l0^–4 and LPSU (P < l0^–8) subgroups.There was virtually no difference in the prevalence of the Alallele between LSA and MPSU subgroups. None of the specificmedical or neuropsychiatric complications of alcoholism wasassociated with the Al allele. In conclusion, the severity ofalcohol dependence in alcoholics and of substance use behaviorsin controls are important variables in DRD2 allelic association.The present report and converging lines of evidence suggestthat the DRD2 locus could represent a prominent gene risk factorfor susceptibility to severe alcoholism. However, other genesand environmental factors, when combined, still play the largerrole.     

Polymorphisms for vinyl chloride metabolism in French vinyl chloride workers

Genetic polymorphisms of aldehyde dehydrogenase 2 (ALDH2) and cytochrome P450 2E1 (CYP2E1) have been shown to influence the degree of genetic damage in Taiwanese workers exposed to the carcinogen - vinyl chloride(VC). Certain French VC workers have been found to express biomarkers of mutant forms of cancer-related proteins (ras-p21 and p53) that have been related to their exposure. ALDH2 and CYP2E1 polymorphisms were investigated in 211 of these workers in an attempt to correlate differences in VC metabolic capacity with differences in the presence of these biomarkers. All of the workers were found to have the normal, wild-type ALDH2 gene, and none of them were found to be homozygous for the variant CYP2E1 allele. Sixteen workers were found to be heterozygous for the variant CYP2E1 allele. After adjusting for age, smoking, drinking and cumulative VC exposure, the odds ratio for the presence of either the mutant ras-p21 or the mutant p53 biomarker in these heterozygous workers was found to be statistically significantly increased in comparison to their homozygous, wild-type counterparts (OR = 5.05; 95% CI = 1.10-23.25). However, as opposed to the case in Taiwanese workers, these polymorphisms are relatively uncommon, and thus differences in ALDH2 and CYP2E1 can account for only a small proportion of the variability in mutagenic response to VC exposure in a Caucasian population.     

ALDEHYDE DEHYDROGENASE ACTIVITY AND ACETATE PRODUCTION BY AEROBIC BACTERIA REPRESENTING THE NORMAL FLORA OF HUMAN LARGE INTESTINE

We have recently proposed the existence of a bacteriocolonicpathway for ethanol oxidation, i.e ethanol is oxidized by alcoholdehydrogenase of intestinal bacteria resulting in high intracoloniclevels of reactive and toxic acetaldehyde. This study was aimedto examine aldehyde dehydrogenase (ALDH) activity, acetaldehydeconsumption and production of acetate by aerobic bacteria (n=27),representing the normal human colonic flora. Most bacterialstrains did not show any membrane-associated aldehyde dehydrogenase,but possessed marked cytosolic NADP⁺- and NAD⁺-dependent aldehydedehydrogenase activity, ranging from 155 nmol of NAD(P)H produced/min/mgof protein to zero with acetaldehyde as substrate. NADP⁺-linkedALDH activity was significantly higher than NAD⁺-linked activityin most of the tested bacteria. In addition, aerobic bacteriametabolized acetaldehyde effectively in vitro and this couldbe inhibited by cyanamide in nearly half of the tested strains.Production of acetate from acetaldehyde ranged from 2420 nmol/10⁹colony-forming units to almost negligible. In conclusion, manyhuman aerobic colonic bacteria possess significant aldehydedehydrogenase activity and can, consequently, produce acetatefrom acetaldehyde in vitro at least under the partially aerobicconditions proposed to prevail on the colonic mucosal surface.Individual variation in the capability of colonic flora to removetoxic acetaldehyde may be one factor regulating intracolonicacetaldehyde levels, as well as the rate of bacteriocolonicpathway for ethanol oxidation.     

A comparison of Val81Met and other polymorphisms of alcohol metabolising genes in patients and controls in Northern Spain

The aim of this paper is to study polymorphism in the TH, ADH1B, ADH1C, ALDH2 and CYP2E1 genes so as to ascertain whether it is associated with excessive consumption of alcohol. The SNPs rs6356 of TH, rs1229984, rs2066702 of ADH1B; rs698, rs1693482 of ADH1C; rs671 of ALDH2; rs72559710, rs55897648, rs6413419, rs3813867, rs2031920, rs6413432 of CYP2E1 were studied in a sample of 172 high-level patients and 150 fully non-drinkers controls. Genotyping was performed using Rt-PCR with Taqman probes. SNPs located at ALDH2 and CYP2E1 showed no heterozygosity. Frequency distribution showed significant differences between the two groups studied for loci TH and ADH1B. The genotype Val/Val of TH locus increased in risk 1.988 times (95% CI: 1.006–3.930) that the subjects carrying the genotype Met/Met; and the genotype ADH1B*1/*1 of ADH1B locus increased in risk 3.811 times (CI: 1.660–8.749) that the subjects carrying the genotype ADH1B*1/*2. Alleles Val and ADH1B*1 may therefore increase the risk of the onset and development of this illness.     

ALDH2和CYP2E1基因多态性及饮酒习惯与肝细胞癌易感性的关系

目的研究乙醛脱氢酶2(ALDH2)和细胞色素P4502E1(CYP2E1)基因多态性与饮酒因素交互作用在广西原发性肝细胞癌发生中的作用。方法对广西壮族自治区300例肝细胞癌和292例正常对照进行流行病学调查研究,并用PCR-RFLP方法检测ALDH2和CYP2E1基因型。结果病例和对照组中ALDH2和CYP2E1变异基因型携带者分别占50.3%、48.0%和32.3%、32.9%(P0.05)。饮酒频度每周≥3次(高频饮酒)且携带变异基因ALDH2和CYP2E1者发生肝癌的危险度分别是饮酒频度每周3次(低频饮酒)且携带野生基因型者的3.334倍(95%CI=1.746～6.406)和1.803倍(95%CI=0.974～3.336),同时携带两变异基因型者患肝癌风险为1.200倍(95%CI=0.730～1.972),且饮酒增加两变异基因型携带者的肝癌发病风险(OR=1.816,95%CI=0.985～3.348)。结论单一ALDH2或CYP2E1基因型与肝细胞癌易感性无关;但高频饮酒且携带变异基因ALDH2或CYP2E1者患肝癌风险增加,且两变异基因型单倍体增加肝癌发病风险。提示乙醇在增加肝癌发病风险的过程中存在基因-环境和基因-基因相互作用。     

The novel micro-opioid receptor antagonist, [N-allyl-Dmt(1)]endomorphin-2, attenuates the enhancement of GABAergic neurotransmission by ethanol

Aims: We investigated the effects of [N-allyl-Dmt¹]endomorphin-2(TL-319), a novel and highly potent µ-opioid receptorantagonist, on ethanol (EtOH)-induced enhancement of GABA_A receptor-mediatedsynaptic activity in the hippocampus. Methods: Evoked and spontaneousinhibitory postsynaptic currents (eIPSCs and sIPSCs) were isolatedfrom CA1 pyramidal cells from brain slices of male rats usingwhole-cell patch-clamp techniques. Results: TL-319 had no effecton the baseline amplitude of eIPSCs or the frequency of sIPSCs.However, it induced a dose-dependent suppression of an ethanol-inducedincrease of sIPSC frequency with full reversal at concentrationsof 500 nM and higher. The non-specific competitive opioid receptorantagonist naltrexone also suppressed EtOH-induced increasesin sIPSC frequency but only at a concentration of 60 µM.Conclusion: These data indicate that blockade of µ-opioidreceptors by low concentrations of [N-allyl-Dmt¹]endomorphin-2can reverse ethanol-induced increases in GABAergic neurotransmissionand possibly alter its anxiolytic or sedative effects. Thissuggests the possibility that high potency opioid antagonistsmay emerge as possible candidate compounds for the treatmentof ethanol addiction.     

PLATELET AFFINITY FOR SEROTONIN IS INCREASED IN ALCOHOLICS AND FORMER ALCOHOLICS: A BIOLOGICAL MARKER FOR DEPENDENCE?

The kinetics of ³H serotonin platelet uptake were studied inalcoholics and former alcoholics to see whether differencesfound between alcohol-preferring and non-preferring rats couldbe reproduced in man. Three groups of patients were studied:10 dependent alcoholics on admission for treatment; 10 dependentalcoholics after 20 days of treatment; 8 former dependent alcoholics,abstinent for 1–11 years. Controls were non-alcoholics,matched for age and sex. The K_m for ³H serotonin uptake in platelets was lower in patientsfrom all three groups compared to 15 controls. This phenomenon could be congenital or induced by the previousexcessive intake of alcohol. We believe that this increased platelet affinity for serotonin,in the absence of cirrhosis of the liver and/or depression couldbe a marker for alcohol dependence, enabling the therapeuticeffort to be focussed on these patients.     

CHARACTERIZATION OF RAT TESTICULAR ALCOHOL DEHYDROGENASE

A protein from rat testes that catalyzes the oxidation of ethanolin the presence of NAD⁺, but not NADP⁺, has been characterizedenzymatically and compared to that of hepatic alcohol dehydrogenaseobtained from the same animals. The testicular enzyme, likethe hepatic enzyme, has a K_m value for ethanol in the 0.5–1.0-mMrange and can utilize other alcohols such as n-propanol, n-butanol,and isobutanol, although the K_m values for these other alcoholsare considerably lower (0.03–0.08 mM) that that for ethanol.The testicular enzyme is more heat-labile than is the hepaticenzyme. Finally, the testicular enzyme catalyzes the oxidationof retinol and its retinol dehydrogenase activity is inhibitedby ethanol.     

REGULATION OF RAT NEURONAL NITRIC OXIDE SYNTHASE ACTIVITY BY CHRONIC ALCOHOLIZATION

Rat neuronal nitric oxide (NO) synthase (nNOS) activity wasmeasured in frontal cortex, hippocampus, striatum and cerebellumusing the assay of [³H]citrulline, following chronic alcoholization.The K_m and V_max values were significantly increased in the frontalcortex and in the striatum, and were not affected in the cerebellumand hippocampus.