Developmental profile of hepatic alcohol and aldehyde dehydrogenase activities in long-sleep and short-sleep mice

Ethanol is metabolized primarily in the liver by a cytosolic alcohol dehydrogenase (ADH). The product, acetaldehyde, is metabolized to acetate by nonspecific aldehyde dehydrogenases (AHD). Mouse liver contains five major constitutive AHD isoenzymes: mitochondrial high Km (AHD-1), mitochondrial low Km (AHD-5), cytosolic high Km (AHD-7), cytosolic low Km (AHD-2) and microsomal high Km (AHD-3). The Long-Sleep (LS) and Short-Sleep (SS) mice differ in their sleep time response to ethanol as early as 10 days of age, and this difference increases with increasing age. Age- and genotype-related differences in metabolism could account for the pattern of responses seen in these mice. We measured the activity of hepatic ADH and the five AHD isoenzymes in LS and SS mice from 3 days of age to adulthood to determine if there were differences in the developmental profiles of these enzyme activities. We found no sex differences in the developmental profile of either ADH or AHD, and the LS and SS mice have nearly identical ADH and AHD activities with the possible exception of the high Km mitochondrial enzyme activity between days 3 and 6, and the low Km mitochondrial enzyme between days 28 and 32. Thus, it appears that differences in ethanol or acetaldehyde metabolism do not contribute significantly to the differential sensitivity to ethanol between young LS and SS mice or to the differential sensitivity between young and adult mice.     

Human liver aldehyde dehydrogenase: subcellular distribution in alcoholics and nonalcoholics

Activity assay and isoelectric focusing analysis of human biopsy and autopsy liver specimens showed the existence of two major aldehyde dehydrogenases (ALDH I, ALDH II). Subcellular distribution of these isozymes was determined in autopsy livers from alcoholics and nonalcoholics. Nearly 70% of the total ALDH activity was recovered in the cytosol which contained both the major isozymes. Densitometric evaluation of isozyme bands showed that about 65% of the cytosolic enzyme activity was due to ALDH II and the rest due to ALDH I isozyme. Only about 5% of the total ALDH activity was found in the mitochondrial fraction (70% ALDH I and 30% ALDH II). Significantly reduced total and specific ALDH activities were noted in all the subcellular fractions from cirrhotic liver specimens. Apparently, ALDH I isozyme from cytosol and mitochondria is primarily responsible for the oxidation of small amounts of acetaldehyde normally found in the blood of nonalcoholics after drinking moderate amounts of alcohol. However, in alcoholics who exhibit higher blood acetaldehyde concentrations after drinking alcohol, ALDH II isozyme may be of greater physiological significance.     

Studies with cDNA probes on the in vivo effect of ethanol on expression of the genes of alcohol metabolism

Mice (Mus musculus) from three genetic strains with variable responses to ethanol challenge (BALB/c, C57BL/6J and 129/ReJ) were used to evaluate the effect of ethanol feeding on hepatic mRNA specific to the two primary enzymes of ethanol metabolism; alcohol dehydrogenase (ADH; E.C. 1.1.1.1) and aldehyde dehydrogenase (ALDH; E.C. 1.2.1.3). Adh-1 (ADH) and Ahd-2 (ALDH) specific mRNA were evaluated on the livers of ethanol-fed mice and from their age, sex and genotype matched controls (using an isocaloric liquid diet). C57BL/6J (alcohol resistant) mice show a significant (approx. 200%) increase in ADH-1 mRNA levels after ethanol treatment, compared to their matched controls. BALB/c (alcohol sensitive) mice have approximately a 20% increase with ethanol treatment while 129/ReJ (alcohol sensitive) mice show a slight reduction in the ADH-1 specific mRNA following ethanol feeding. A strain-specific pattern is also apparent in the AHD-2 mRNA as a result of ethanol feeding in the experimental animals. C57BL/6J mice have an increase and BALB/c mice show no apparent change in the AHD-2 mRNA. 129/ReJ mice fed an ethanol diet, on the other hand, appear to have a decrease in the level of AHD-2 hepatic mRNA as compared to their matched controls. The relative mRNA levels of the two genes correlate well with the respective enzyme activity levels, but for mice on the control diet only. Ethanol feeding, which causes an apparent reduction in hepatic ADH enzyme activity in BALB/c and 129/ReJ and an apparent increase in ALDH activity in C57BL/6J (under the experimental protocols used) also alters the mRNA levels specific to the two genes. However, changes in the mRNA levels after ethanol feeding cannot be directly related to the changes seen in enzyme activity. The observed steady state level of AHD-2 mRNA and the increase in ALDH activity after ethanol feeding, which is unique to C57BL/6J mice, is expected to offer a faster clearance (metabolism) of acetaldehyde, the toxic metabolite, and may be responsible for, or contribute to, the relative resistance of this strain to ethanol.     

Basis of aldehyde dehydrogenase deficiency in Orientals: immunochemical studies

While most Caucasians have two main isozymes of liver aldehyde dehydrogenase, in about 50% of Orientals the ALDH I isozyme is missing. This isozyme, which has a faster electrophoretic mobility, is predominantly present in mitochondria and has a relatively low Km for acetaldehyde. The inherent deficiency of ALDH I is responsible for the impaired acetaldehyde oxidation leading to facial flushing and other cardiovascular symptoms of alcohol sensitivity commonly observed in Japanese and Chinese. Antibodies raised against apparently homogeneous liver ALDH I and ALDH II isozymes did not show an immunological similarity between the two isozymes which do not share common subunits. While erythrocyte ALDH II is also immunologically distinct from hepatic ALDH I, it showed an immunological similarity with hepatic ALDH II. On isoelectric focusing in agarose gel followed by immunoelectrophoresis, at least 4 components with an anti-ALDH I antibody were detected in extracts from Caucasian and Oriental livers. In Japanese livers deficient in ALDH I activity, the prominent ALDH component was missing. Apparently, more than one gene is responsible for the synthesis of ALDH isozymes reacting with an antibody against ALDH I. A deletion in one of the genes may be responsible for the loss of ALDH I enzyme activity and altered antigenic properties. However, at this stage, a point mutation in a structural gene coding for ALDH I resulting in a defective protein with altered electrophoretic and enzymatic properties is not ruled out.     

Ethanol feeding can produce secondary alterations in aldehyde dehydrogenase isozymes

Depressed hepatic aldehyde dehydrogenase (ALDH) activity levels have been observed in alcoholics, but whether the deficit is primary or secondary in nature remains controversial. In this study, we examined liver ALDH in rodent (rat) and primate (baboon) animal models pair-fed nutritionally adequate ethanol or isocaloric carbohydrate containing liquid diets. Both species show qualitative changes in ALDH isozymes after ethanol consumption. The changes include alterations in isozyme patterns seen upon electrofocusing and decreased responsiveness to the ALDH inhibitor, disulfiram. The subcellular locus of most of the changes is cytosolic in the baboon and mitochondrial in the rat. Study of partially purified (enriched) baboon cytosolic ALDH confirmed changes seen in the original cytosols and kinetic characterization of the enriched enzyme revealed a 9-fold higher Km for acetaldehyde in ALDH from an ethanol treated animal. We note that qualitative and quantitative changes secondary to ethanol treatment in the primate model closely parallel those described in human alcoholics.     

Determination of aldehyde dehydrogenase isozyme activity in human liver

As acetaldehyde (Ac-CHO) has been implicated as a cause of alcoholic liver injury, accurate knowledge concerning changes in the Ac-CHO oxidizing system in human liver is essential for the understanding of the pathogenesis. However, an assay system for aldehyde dehydrogenase (ALDH: EC 1.2, 1.3) isozymes in human biological material has not yet been established. In the present study, the assay systems for human liver ALDH isozyme activity were analyzed. In human red blood cells, in which only one type of ALDH isozyme, high Km ALDH, is present, a maximum activity was observed at a substrate concentration of over 300 microM. In human liver of the usual type in which ALDH I (low Km isozyme) was not deficient, the activity reached a first plateau at 12 microM Ac-CHO after which the activity started to increase again at 20 microM Ac-CHO and continued to increase until 5.0 mM Ac-CHO. In the liver of the unusual type, which is deficient in low Km ALDH, activity was not detected at Ac-CHO concentrations lower than 10 microM. These results indicate that the optimum substrate concentrations for the determination of ALDH isozymes are 12 microM for low Km, 300 microM for high Km and over 1 mM for very high Km ALDH isozymes. The maximum activities of these three isozymes in the liver were obtained at a pH ranging between 9.0-9.5 and at an NAD concentration of over 500 microM. From these results, it is concluded that the assay system of Blair and Bodley is applicable for the determination of ALDH isozyme activity in human biological material with the exception of determining Km values.     

Aldehyde dehydrogenases, aldehyde oxidase and xanthine oxidase from baboon tissues: phenotypic variability and subcellular distribution in liver and brain

Isoelectric focusing (IEF) and cellulose acetate electrophoresis were used to examine the multiplicity and distribution of aldehyde dehydrogenases (ALDHs), aldehyde oxidase (AOX) and xanthine oxidase (XOX) from tissues of olive and yellow baboons. Five ALDHs were resolved and distinguished on the basis of their differential tissue and subcellular distribution or substrate specificity. Some ALDHs exhibited multiple activity zones. Baboon liver ALDHs were differentially distributed in cytosol (ALDHs II, III and V) and large granular (mitochondrial) fractions (ALDHs I and IV). The major liver ALDHs (I and II) were also broadly distributed in other tissues, as was the major stomach enzyme (ALDH-III). Three brain ALDHs were resolved, which were also differentially distributed between large granular (mitochondrial) (ALDHs I and IV) and cytosolic (ALDH-III) fractions. Electrophoretic variability between individuals was observed for the major liver mitochondrial isozyme (ALDH-I), the major stomach isozyme (ALDH-III) and the minor liver isozymes (ALDHs IV and V). Single forms of AOX and XOX were found in baboon tissue extracts, with the highest activities in liver (AOX) and intestine extracts (XOX). Both oxidases were predominantly localized in the liver soluble fraction.     

Research on alcohol metabolism among Asians and its implications for understanding causes of alcoholism

Research into the causes of alcoholism is a relatively recent scientific endeavor. One area of study which could lead to better understanding of the disease is the possibility of a genetic predisposition to alcoholism. Recent work has demonstrated that people have varying complements of enzymes to metabolize alcohol. Current knowledge is examined about the influence of various ethanol metabolizing enzymes on alcohol consumption by Asians and members of other ethnic groups. The two principal enzymes involved in ethanol oxidative metabolism are alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). ADH is responsible for the metabolism of ethanol to acetaldehyde. ALDH catalyzes the conversion of acetaldehyde to acetate. The different isozymes account for the diversity of alcohol metabolism among individuals. An isozyme of ADH (beta 2 beta 2) is found more frequently in Asians than in whites, and an ALDH isozyme (ALDH2), although present in Asians, often is in an inactive form. The presence of an inactive form of ALDH2 is thought to be responsible for an increase in acetaldehyde levels in the body. Acetaldehyde is considered responsible for the facial flushing reaction often observed among Asians who have consumed alcohol. A dysphoric reaction to alcohol, producing uncomfortable sensations, is believed to be a response to deter further consumption. Although the presence of an inactive ALDH2 isozyme may serve as a deterrent to alcohol consumption, its presence does not fully explain the levels of alcohol consumption by those with the inactive isozyme. Other conditions, such as social pressure, and yet undetermined biological factors, may play a significant role in alcohol consumption.     

Purification and partial characterization of acetyl-coA synthetase in rat liver mitochondria

Acetyl-CoA synthetase (AceCS), which catalyzes the activation of acetate to produce acetyl-CoA, was found to have a much greater Km value for acetate in liver mitochondria than that in the heart mitochondria of rats, indicating that two different types of AceCS are located in the liver and heart mitochodria. Recently, Fujino et al. reported that mouse heart mitochondrial AceCS, designated AceCS2, was expressed in a wide range of tissues, however, it was apparently absent from the liver. In this study, liver mitochondrial AceCS activity, but not heart AceCS2, was greatly induced in di(2-ethylhexyl)phthalate (DEHP)-treated rats. We purified and characterized the rat liver mitochondrial AceCS. The molecular mass of the enzyme estimated by SDS-PAGE was -58 kDa, which was quite different from that of the heart mitochondrial enzyme, AceCS2. The calculated Km value for the acetate of the partially purified liver enzyme was much greater, being about 100 times that of heart enzyme, AceCS2.     

Biochemical genetic analysis of human and rodent aldehyde dehydrogenase (ALDH)

ALDH isozymes have been characterized in terms of substrate and coenzyme specificity, heat stability, tissue distribution and electrophoretic properties. The activity of the isozymes has also been examined in rodent-human somatic cell hybrids in order to map the structural genes to specific chromosomes and to study the control of gene expression. One isozyme, designated ALDH3, which is very active against benzaldehyde, was found to show variable expression in hybrids made between rat hepatoma cells and human fibroblasts or fetal liver. Segregation analysis of these hybrids indicates that the structural locus for human ALDH3 may be on chromosome 17. The expression of rodent ALDH3 in these hybrids was extremely variable and not correlated with the appearance of the human enzyme. In hybrids expressing human and rodent ALDH3 no heteromeric isozymes were observed. The human "cytosolic" ALDH1 and "mitochondrial" ALDH2 isozymes did not appear to be expressed in any of the somatic cell hybrids examined.     

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.     

Overview of the role of alcohol dehydrogenase and aldehyde dehydrogenase and their variants in the genesis of alcohol-related pathology

Alcohol dehydrogenase (ADH) and mitochondrial aldehyde dehydrogenase (ALDH2) are responsible for metabolizing the bulk of ethanol consumed as part of the diet and their activities contribute to the rate of ethanol elimination from the blood. They are expressed at highest levels in liver, but at lower levels in many tissues. This pathway probably evolved as a detoxification mechanism for environmental alcohols. However, with the consumption of large amounts of ethanol, the oxidation of ethanol can become a major energy source and, particularly in the liver, interferes with the metabolism of other nutrients. Polymorphic variants of the genes for these enzymes encode enzymes with altered kinetic properties. The pathophysiological effects of these variants may be mediated by accumulation of acetaldehyde; high-activity ADH variants are predicted to increase the rate of acetaldehyde generation, while the low-activity ALDH2 variant is associated with an inability to metabolize this compound. The effects of acetaldehyde may be expressed either in the cells generating it, or by delivery of acetaldehyde to various tissues by the bloodstream or even saliva. Inheritance of the high-activity ADH beta2, encoded by the ADH2*2 gene, and the inactive ALDH2*2 gene product have been conclusively associated with reduced risk of alcoholism. This association is influenced by gene-environment interactions, such as religion and national origin. The variants have also been studied for association with alcoholic liver disease, cancer, fetal alcohol syndrome, CVD, gout, asthma and clearance of xenobiotics. The strongest correlations found to date have been those between the ALDH2*2 allele and cancers of the oro-pharynx and oesophagus. It will be important to replicate other interesting associations between these variants and other cancers and heart disease, and to determine the biochemical mechanisms underlying the associations.     

五株三带喙库蚊的酯酶同工酶比较研究

本文应用聚丙烯酰胺凝胶电泳(PAGE)和等电聚焦电泳(IEF)的方法对我国5个三带喙库蚊地区株的酯酶同工酶(EST.)进行了比较研究。结果表明,不同三带喙库蚊地区株的酯酶同工酶在PAGE上表现出3个位点共12条酶带,在IEF上表现出26条酶带。各地区株群体间的EST无显著性差异。     

Inhibition of human alcohol and aldehyde dehydrogenases by acetaminophen: Assessment of the effects on first-pass metabolism of ethanol

Acetaminophen is one of the most widely used over-the-counter analgesic, antipyretic medications. Use of acetaminophen and alcohol are commonly associated. Previous studies showed that acetaminophen might affect bioavailability of ethanol by inhibiting gastric alcohol dehydrogenase (ADH). However, potential inhibitions by acetaminophen of first-pass metabolism (FPM) of ethanol, catalyzed by the human ADH family and by relevant aldehyde dehydrogenase (ALDH) isozymes, remain undefined. ADH and ALDH both exhibit racially distinct allozymes and tissue-specific distribution of isozymes, and are principal enzymes responsible for ethanol metabolism in humans. In this study, we investigated acetaminophen inhibition of ethanol oxidation with recombinant human ADH1A, ADH1B1, ADH1B2, ADH1B3, ADH1C1, ADH1C2, ADH2, and ADH4, and inhibition of acetaldehyde oxidation with recombinant human ALDH1A1 and ALDH2. The investigations were done at near physiological pH 7.5 and with a cytoplasmic coenzyme concentration of 0.5 mm NAD⁺. Acetaminophen acted as a noncompetitive inhibitor for ADH enzymes, with the slope inhibition constants (K_is) ranging from 0.90 mm (ADH2) to 20 mm (ADH1A), and the intercept inhibition constants (K_ii) ranging from 1.4 mm (ADH1C allozymes) to 19 mm (ADH1A). Acetaminophen exhibited noncompetitive inhibition for ALDH2 (K_is = 3.0 mm and K_ii = 2.2 mm), but competitive inhibition for ALDH1A1 (K_is = 0.96 mm). The metabolic interactions between acetaminophen and ethanol/acetaldehyde were assessed by computer simulation using inhibition equations and the determined kinetic constants. At therapeutic to subtoxic plasma levels of acetaminophen (i.e., 0.2–0.5 mm) and physiologically relevant concentrations of ethanol (10 mm) and acetaldehyde (10 μm) in target tissues, acetaminophen could inhibit ADH1C allozymes (12–26%) and ADH2 (14–28%) in the liver and small intestine, ADH4 (15–31%) in the stomach, and ALDH1A1 (16–33%) and ALDH2 (8.3–19%) in all 3 tissues. The results suggest that inhibition by acetaminophen of hepatic and gastrointestinal FPM of ethanol through ADH and ALDH pathways might become significant at higher, subtoxic levels of acetaminophen.     

Protein adduct species in muscle and liver of rats following acute ethanol administration

AIMS: Previous immunohistochemical studies have shown that the post-translational formation of aldehyde-protein adducts may be an important process in the aetiology of alcohol-induced muscle disease. However, other studies have shown that in a variety of tissues, alcohol induces the formation of various other adduct species, including hybrid acetaldehyde-malondialdehyde-protein adducts and adducts with free radicals themselves, e.g. hydroxyethyl radical (HER)-protein adducts. Furthermore, acetaldehyde-protein adducts may be formed in reducing or non-reducing environments resulting in distinct molecular entities, each with unique features of stability and immunogenicity. Some in vitro studies have also suggested that unreduced adducts may be converted to reduced adducts in situ. Our objective was to test the hypothesis that in muscle a variety of different adduct species are formed after acute alcohol exposure and that unreduced adducts predominate. METHODS: Rabbit polyclonal antibodies were raised against unreduced and reduced aldehydes and the HER-protein adducts. These were used to assay different adduct species in soleus (type I fibre-predominant) and plantaris (type II fibre-predominant) muscles and liver in four groups of rats administered acutely with either [A] saline (control); [B] cyanamide (an aldehyde dehydrogenase inhibitor); [C] ethanol; [D] cyanamide+ethanol. RESULTS: Amounts of unreduced acetaldehyde and malondialdehyde adducts were increased in both muscles of alcohol-dosed rats. However there was no increase in the amounts of reduced acetaldehyde adducts, as detected by both the rabbit polyclonal antibody and the RT1.1 mouse monoclonal antibody. Furthermore, there was no detectable increase in malondialdehyde-acetaldehyde and HER-protein adducts. Similar results were obtained in the liver. CONCLUSIONS: Adducts formed in skeletal muscle and liver of rats exposed acutely to ethanol are mainly unreduced acetaldehyde and malondialdehyde species.     

Effect of acetaldehyde on binding of prostaglandins by receptors of liver plasma membranes

Rat liver plasma membranes possess a single class of high affinity binding sites for the carbonyl-containing prostaglandins PGE2 and PGE1. The specificity of the binding sites is confirmed by the effective competition of the corresponding unlabeled PGs with 3H-PGs for binding sites on receptors. The modification of liver plasma membranes by acetaldehyde drastically decreases the density of the binding sites, leaving unaffected the affinity of receptors. To bind PGF2 alpha, liver plasma membranes have two types of binding sites, strong and weak ones. The alkylation of membranes by acetaldehyde does not essentially change the PGF2 alpha binding parameters. It is suggested that the protective effect of PGs in alcoholic liver injury occurs by their competition with acetaldehyde for binding sites on specific PG-binding receptors of liver plasma membranes.     

A physiologically based model for ethanol and acetaldehyde metabolism in human beings.

Pharmacokinetic models for ethanol metabolism have contributed to the understanding of ethanol clearance in human beings. However, these models fail to account for ethanol's toxic metabolite, acetaldehyde. Acetaldehyde accumulation leads to signs and symptoms, such as cardiac arrhythmias, nausea, anxiety, and facial flushing. Nevertheless, it is difficult to determine the levels of acetaldehyde in the blood or other tissues because of artifactual formation and other technical issues. Therefore, we have constructed a promising physiologically based pharmacokinetic (PBPK) model, which is an excellent match for existing ethanol and acetaldehyde concentration-time data. The model consists of five compartments that exchange material: stomach, gastrointestinal tract, liver, central fluid, and muscle. All compartments except the liver are modeled as stirred reactors. The liver is modeled as a tubular flow reactor. We derived average enzymatic rate laws for alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH), determined kinetic parameters from the literature, and found best-fit parameters by minimizing the squared error between our profiles and the experimental data. The model's transient output correlates strongly with the experimentally observed results for healthy individuals and for those with reduced ALDH activity caused by a genetic deficiency of the primary acetaldehyde-metabolizing enzyme ALDH2. Furthermore, the model shows that the reverse reaction of acetaldehyde back into ethanol is essential and keeps acetaldehyde levels approximately 10-fold lower than if the reaction were irreversible.     

Aldehyde dehydrogenase content and composition of human liver

Human liver contains only four proteins which catalyze dehydrogenation of acetaldehyde; two of these are tetrameric with MW of 220,000 and are structurally related. These enzymes were purified previously to homogeneity and are now known as the cytoplasmic E1 and mitochondrial E2. The other two proteins do not appear to be structurally related to E1 and E2. The recently isolated E4 enzyme is a dimer of MW of ca. 175,000; the E3 may be a polymorphic enzyme. The Enzyme Commission classification for E1 and E2 is EC 1.2.1.3, that for E4 is at present uncertain since its Michaelis constants for short chain aldehydes are high, making it unlikely that these would be its natural substrates. The relationship between E3 and E4 is also uncertain. Employing a suitably designed assay, E1 and E2 are assayed as "low Km" enzymes while E3 and E4 are assayed as "high Km" enzymes. Therefore by employing such an assay, combined with electrofocusing procedure, an assessment of enzyme content and composition of aldehyde dehydrogenase in human liver can be made.     

Use of cyanamide to determine localization of acetaldehyde metabolism in rat liver

Various techniques have been employed previously to show that acetaldehyde is primarily oxidized in the mitochondrial matrix of rat liver. In this study, a new approach was tested. Mitochondrial low-Km aldehyde dehydrogenase (ALDH) was partially inactivated and the effect on acetaldehyde oxidation measured. Cyanamide was chosen as the ALDH inhibitor. An enzymatic activation of cyanamide, probably by catalase, was necessary for the drug to inhibit ALDH activity. The level of remaining ALDH activity after cyanamide treatment was correlated with the ability of either rat liver mitochondria or liver slices to oxidize acetaldehyde. Any inhibition of ALDH resulted in a decreased rate of acetaldehyde oxidation, indicating that there is no excess of ALDH in the cell above what is needed to oxidize acetaldehyde. Approximately 15% of the acetaldehyde disappearance at 200 microM was catalyzed by high-Km ALDH, and nearly 30% of the acetaldehyde was lost through binding to cytosolic proteins.     

Allozyme diversity in Anopheles quadrimaculatus (sensu stricto) populations in northeastern Arkansas

A comparison of electrophoretically detectable isozyme differences in 6 populations of Anopheles quadrimaculatus (sensu stricto) from northeastern Arkansas was undertaken to test the hypothesis that microgeographic variation in habitat types was promoting significant within- and between-population genetic diversity. Genetic heterogeneity within populations was substantial, with all of the enzyme loci examined having 2-7 alleles and average levels of polymorphisms per population between 54.5 and 72.7%. Heterozygotes made up an average over all loci of between 20.6 and 24.8% of the individuals examined. Only weak evidence was found for gametic disequilibrium between pairs of loci. Neither F-statistic nor genetic distance analysis suggested interpopulation divergence. The FST value averaged over loci was 0.190. All Nei distances for pair-wise population comparisons were greater than 0.010, which was much lower than published values from comparisons between populations belonging to different species of the complex. Divergence was not significantly correlated to either geographic distance or habitat type. Examination of the results suggests that little genetic divergence has occurred between populations of An. quadrimaculatus in northeastern Arkansas, possibly because of the dispersal ability and low level of discrimination between oviposition sites exhibited by this species.