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X Parés

Publications and source records attributed to X Parés.

At least 37 records · Page 2Linked to original sources
PubMed1996

Molecular modelling of human gastric alcohol dehydrogenase (class IV) and substrate docking: differences towards the classical liver enzyme (class I).

A three-dimensional model of the human class IV alcohol dehydrogenase has been calculated based upon the X-ray structure of the class I enzyme. As judged from the model, the substrate-binding site is wider than in class I, compatible with the differences in substrate specificities and the large difference in Km value for ethanol. Substrate docking performed for the class I structure and the class IV model show all-trans-retinol and 11-cis-retinol to bind better to the class IV enzyme. The calculations also indicate that 16-hydroxyhexadecanoic acid binds in a different manner for the two enzyme classes. A simulation of coenzyme-binding indicates that the adenine ring of the coenzyme might be differently bound in class IV than in class I, decreasing the interactions with Asp-223 which is compatible with the higher k(cat) values for class IV.

Alcohol Dehydrogenase↗
PubMed1996

Pea formaldehyde-active class III alcohol dehydrogenase: common derivation of the plant and animal forms but not of the corresponding ethanol-active forms (classes I and P).

A plant class III alcohol dehydrogenase (or glutathione-dependent formaldehyde dehydrogenase) has been characterized. The enzyme is a typical class III member with enzymatic parameters and substrate specificity closely related to those of already established animal forms. Km values with the pea enzyme are 6.5 microM for NAD+, 2 microM for S-hydroxymethylglutathione, and 840 microM for octanol versus 9, 4, and 1200 microM, respectively, with the human enzyme. Structurally, the pea/human class III enzymes are closely related, exhibiting a residue identity of 69% and with only 3 of 23 residues differing among those often considered in substrate and coenzyme binding. In contrast, the corresponding ethanol-active enzymes, the long-known human liver and pea alcohol dehydrogenases, differ more (47% residue identities) and are also in functionally important active site segments, with 12 of the 23 positions exchanged, including no less than 7 at the usually much conserved coenzyme-binding segment. These differences affect functionally important residues that are often class-distinguishing, such as those at positions 48, 51, and 115, where the plant ethanol-active forms resemble class III (Thr, Tyr, and Arg, respectively) rather than the animal ethanol-active class I forms (typically Ser, His, and Asp, respectively). Calculations of phylogenetic trees support the conclusions from functional residues in subgrouping plant ethanol-active dehydrogenases and the animal ethanol-active enzymes (class I) as separate descendants from the class III line. It appears that the classical plant alcohol dehydrogenases (now called class P) have a duplicatory origin separate from that of the animal class I enzymes and therefore a paralogous relationship with functional convergence of their alcohol substrate specificity. Combined, the results establish the conserved nature of class III also in plants, and contribute to the molecular and functional understanding of alcohol dehydrogenases by defining two branches of plant enzymes into the system.

Alcohol Dehydrogenase↗
PubMed1995

Class III alcohol dehydrogenase from Saccharomyces cerevisiae: structural and enzymatic features differ toward the human/mammalian forms in a manner consistent with functional needs in formaldehyde detoxication.

Alcohol dehydrogenase class III (glutathione-dependent formaldehyde dehydrogenase) from Saccharomyces cerevisiae was purified and analyzed structurally and enzymatically. The corresponding gene was also analyzed after cloning from a yeast genome library by screening with a probe prepared through PCR amplification. As with class III alcohol dehydrogenase from other sources, the yeast protein was obtained in two active forms, deduced to reflect different adducts/modifications. Protein analysis established N-terminal and C-terminal positions, showing different and specific patterns in protein start positions between the human/mammalian, yeast, and prokaryotic forms. Km values with formaldehyde differ consistently, being about 10-fold higher in the yeast than the human/mammalian enzymes, but compensated for by similar changes in kcat values. This is compatible with the different functional needs, emphasizing low formaldehyde concentration in the animal cells but efficient formaldehyde elimination in the microorganisms. This supports a general role of the enzyme in formaldehyde detoxication rather than in long-chain alcohol turnover.

Alcohol Dehydrogenase↗
PubMed1994

Alcohol dehydrogenase of class IV (sigma sigma-ADH) from human stomach. cDNA sequence and structure/function relationships.

Human stomach mucosa contains a characteristic alcohol dehydrogenase (ADH) enzyme, sigma sigma-ADH. Its cDNA has been cloned from a human stomach library and sequenced. The deduced amino acid sequence shows 59-70% identities with the other human ADH classes, demonstrating that the stomach enzyme represents a distinct structure, constituting class IV, coded by a separate gene, ADH7. The amino acid identity with the rat stomach class IV ADH is 88%, which is intermediate between constant and variable dehydrogenases. This value reflects higher conservation than for the classical liver enzymes of class I, compatible with a separate functional significance of the class IV enzyme. Its enzymic features can be correlated with its structural characteristics. The residues lining the substrate-binding cleft are bulky and hydrophobic, similar to those of the class I enzyme; this explains the similar specificity of both classes, compatible with the origin of class IV from class I. Position 47 has Arg, in contrast to Gly in the rat class IV enzyme, but this Arg is still associated with an extremely high activity (kcat = 1510 min-1) and weak coenzyme binding (KiaNAD+ = 1.6 mM). Thus, the strong interaction with coenzyme imposed by Arg47 in class I is probably compensated for in class IV by changes that may negatively affect coenzyme binding: Glu230, His271, Asn260, Asn261, Asn363. The still higher activity and weaker coenzyme binding of rat class IV (kcat = 2600 min-1, KiaNAD = 4 mM) can be correlated to the exchanges to Gly47, Gln230 and Tyr363. An important change at position 294, with Val in human and Ala in rat class IV, is probably responsible for the dramatic difference in Km values for ethanol between human (37 mM) and rat (2.4 M) class IV enzymes.

Alcohol Dehydrogenase↗
PubMed1994

Mammalian class IV alcohol dehydrogenase (stomach alcohol dehydrogenase): structure, origin, and correlation with enzymology.

The structure of a mammalian class IV alcohol dehydrogenase has been determined by peptide analysis of the protein isolated from rat stomach. The structure indicates that the enzyme constitutes a separate alcohol dehydrogenase class, in agreement with the distinct enzymatic properties; the class IV enzyme is somewhat closer to class I (the "classical" liver alcohol dehydrogenase; approximately 68% residue identities) than to the other classes (II, III, and V; approximately 60% residue identities), suggesting that class IV might have originated through duplication of an early vertebrate class I gene. The activity of the class IV protein toward ethanol is even higher than that of the classical liver enzyme. Both Km and kcat values are high, the latter being the highest of any class characterized so far. Structurally, these properties are correlated with replacements at the active site, affecting both substrate and coenzyme binding. In particular, Ala-294 (instead of valine) results in increased space in the middle section of the substrate cleft, Gly-47 (instead of a basic residue) results in decreased charge interactions with the coenzyme pyrophosphate, and Tyr-363 (instead of a basic residue) may also affect coenzyme binding. In combination, these exchanges are compatible with a promotion of the off dissociation and an increased turnover rate. In contrast, residues at the inner part of the substrate cleft are bulky, accounting for low activity toward secondary alcohols and cyclohexanol. Exchanges at positions 259-261 involve minor shifts in glycine residues at a reverse turn in the coenzyme-binding fold. Clearly, class IV is distinct in structure, ethanol turnover, stomach expression, and possible emergence from class I.

Alcohol Dehydrogenase↗
PubMed1994

Alcohol dehydrogenase from human stomach: variability in normal mucosa and effect of age, gender, ADH3 phenotype and gastric region.

Alcohol dehydrogenase (ADH) has been analysed in 36 endoscopic biopsies of normal gastric body and/or antrum mucosa, from 31 individuals with an age between 17 and 79 years. Oesophageal, duodenal and oral mucosa specimens have been also examined. Stomach mucosa contains three isozyme types: the gamma gamma-ADH forms (class I), sigma sigma-ADH (class IV) and chi chi-ADH (class III). gamma gamma-ADH was present in all gastric samples, while sigma sigma-ADH was detected in all body specimens (n = 15) but only in eight of 20 antrum biopsies. The presence of high sigma sigma-ADH activity in oral and oesophageal mucosa confirms the distribution of class IV in the upper gastrointestinal tract where it may serve as a first metabolic barrier against ingested alcohols and aldehydes. Considering all gastric specimens, ADH activity was 5.78 +/- 2.61 mU/mg of protein with 100 mM ethanol, pH 10.0. ADH activity was higher in men than women and in gastric body than in antrum, although differences did not reach statistical significance. However, activity was significantly higher in subjects below 50 years than those older than 50 years. Furthermore, an inverse correlation was found between gastric ADH activity and age (r = -0.40, P < 0.02). In old subjects ADH activity was significantly higher in gastric body (5.87 +/- 1.22 mU/mg) than in antrum (4.14 +/- 1.78 mU/mg) (P = 0.03). Differences in activity between samples from each ADH3 phenotype were statistically not significant but corresponded to those expected from the kinetic constants of the respective gamma gamma-ADH isozymes, which suggests that ADH3 polymorphism affects activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Genetic polymorphism of liver alcohol dehydrogenase in Spanish subjects: significance of alcohol consumption and liver disease.

Class I alcohol dehydrogenase (ADH) phenotypes have been studied by starch gel electrophoresis and activity analysis in liver tissue obtained at necropsy from 61 non-alcoholic subjects with normal liver (controls), and in biopsies from 60 chronic alcoholics with liver disease and from 24 subjects with non-alcoholic liver disease. Twenty-three per cent of controls exhibited the ADH2 phenotype, which represents the highest frequency for atypical ADH found in a Caucasian population. Both alcoholic and non-alcoholic patients with liver disease showed a lower frequency of the atypical phenotype (6.6% and 8.8%, respectively). No differences in the ADH2 locus were detected among groups of patients with different severity of alcoholic and non-alcoholic liver disease. The allele frequencies of the ADH3 locus for the controls (ADH3 = 0.63, ADH3 = 0.37) are common to those of other Caucasian populations. Similar ADH3 allele frequencies were observed in patients with alcoholic and non-alcoholic liver disease. Discrepancies between the various phenotyping and genotyping studies now known for several populations suggest that local differences may exist in the distribution of the ADH polymorphism in even geographically close regions, and that the effect of ADH polymorphism on vulnerability towards alcohol may not be identical in different populations.

Alcohol Dehydrogenase↗
PubMed1993

Origin of the human alcohol dehydrogenase system: implications from the structure and properties of the octopus protein.

In contrast to the multiplicity of alcohol dehydrogenase in vertebrates, a class III type of the enzyme [i.e., a glutathione-dependent formaldehyde dehydrogenase; formaldehyde; NAD+ oxidoreductase (glutathione-formylating), EC 1.2.1.1.] is the only form detectable in appreciable yield in octopus. It is enzymatically and structurally highly similar to the human class III enzyme, with limited overall residue differences (26%) and only a few conservative residue exchanges at the substrate and coenzyme pockets, reflecting "constant" characteristics of this class over wide time periods. It is distinct from the ethanol-active "variable" class I type of the enzyme (i.e., classical liver alcohol dehydrogenase; alcohol:NAD+ oxidoreductase, EC 1.1.1.1). The residue conservation of class III is also spaced differently from that of class I but is typical of that of proteins in general, emphasizing that class I, with divergence at three functional segments, is the form with deviating properties. In spite of the conservation in class III, surface charges differ considerably. The apparent absence of a class I enzyme in octopus and the constant nature of the class III enzyme support the concept of a duplicative origin of the class I line from the ancient class III form. Still more distant relationships define further enzyme lines that have subunits with other properties.

Alcohol Dehydrogenase↗
PubMed1993

Physiological substrates for rat alcohol dehydrogenase classes: aldehydes of lipid peroxidation, omega-hydroxyfatty acids, and retinoids.

Alcohol dehydrogenase classes exhibit important differences in both substrate specificity and tissue distribution which suggest distinct physiological functions. We have studied the kinetic constants at pH 7.5 of the rat alcohol dehydrogenase classes, purified from liver (classes I and III) and from stomach (class IV), with three groups of relevant physiological compounds: cytotoxic aldehydes generated in lipid peroxidation, omega-hydroxyfatty acids, and retinoids. Classes I and IV actively reduce 4-hydroxynonenal, 2-hexenal, and hexanal, which are toxic compounds known to be produced in significant amounts during lipid peroxidation. Class III shows poor activity with these aldehydes. Class IV exhibits the best kcat/Km values (2150 mM-1 x min-1 for 4-hydroxynonenal), which suggest a role for this enzyme in the elimination of the cytotoxic aldehydes in tissues that are susceptible to lipid peroxidation, such as skin, cornea, and mucosa of the respiratory and digestive tracts, where class IV is localized. The three classes are very active with omega-hydroxyfatty acids, suggesting that all of them are involved in the physiological oxidation of these compounds in the rat tissues. The kinetic constants support that oxidation of omega-hydroxyfatty acids is a physiological function for class III, in addition to its role as formaldehyde dehydrogenase. Finally, classes I and IV are active in retinol oxidation and retinal reduction. Class IV may play a crucial role in the generation of retinoic acid in epithelia, where this compound is involved in development and cell differentiation. In conclusion, alcohol dehydrogenase is an enzyme with multiple metabolic roles, and the different substrate specificity and tissue localization for each class provide organs and tissues with distinct physiological functions.

Alcohol Dehydrogenase↗
PubMed1993

The role of 2',3'-cyclic phosphodiesters in the bovine pancreatic ribonuclease A catalysed cleavage of RNA: intermediates or products?

There is a considerable degree of ambiguity in the literature regarding the role of the 2',3'-cyclic phosphodiesters formed during the reaction of RNA cleavage catalysed by ribonuclease. Usually the reaction is considered to take place in two steps: in the first step there is a transphosphorylation of the RNA 3',5'-phosphodiester bond broken yielding a 2',3'-cyclic phosphodiester which in the second step is hydrolysed to a 3'-nucleotide. Although in many occasions, either explicitly or implicitly, the reaction is treated as taking place sequentially, this is not the case as it has been shown that the 2',3'-phosphodiesters are actually released to the medium as true products of the reaction and that no hydrolysis of these cyclic compounds takes place until all the susceptible 3',5'-phosphodiester bonds have been cyclised. Comparison of the hydrolysis and alcoholysis of the 2',3'-phosphodiesters catalysed by RNase A indicates that the hydrolysis reaction has to be considered formally as a special case of the transphosphorylation back reaction in which the R group of the R-OH substrate is just H. It is thus concluded that the 2',3'-cyclic phosphodiesters formed in the ribonuclease A reaction are true products of the transphosphorylation reaction and not intermediates as usually considered.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1993

Cephalopod alcohol dehydrogenase: purification and enzymatic characterization.

Octopus, squid and cuttle-fish organs were examined for alcohol dehydrogenase activity. Only one form was detectable, with properties typical of mammalian class III alcohol dehydrogenase. The corresponding protein was purified from octopus and enzymatically characterized. Ion-exchange and affinity chromatography produced a pure protein in excellent yield (73%) after 1600-fold purification. Enzymatic parameters with several substrates were similar to those for the human class III alcohol dehydrogenase, demonstrating a largely conserved function of the enzyme through wide lines of divergence covering vertebrates, cephalopods and bacteria. The results establish the universal occurrence of class III alcohol dehydrogenase and its strictly conserved functional properties in separate living forms. The absence of other alcohol dehydrogenases in cephalopods is compatible with the emergence of the ethanol-active class I type at a later stage, in lineages leading to vertebrates.

Alcohol Dehydrogenase↗
PubMed1993

Determinants of ethanol and acetaldehyde metabolism in chronic alcoholics.

We have studied the factors determining the rate of ethanol and acetaldehyde metabolism in a group of 25 alcoholics with varying degrees of liver lesion (from normal liver to cirrhosis) and in six nonalcoholic cirrhotics. In alcoholics the ethanol metabolic rate was related to hepatic function, estimated either by the aminopyrine breath test (r = 0.70, p < 0.001) or the indocyanine green clearance (r = 0.76, p < 0.01), and was independent of the activity of hepatic alcohol dehydrogenase and hepatic blood flow. In nonalcoholic cirrhotics blood acetaldehyde was always below the detection limit (0.5 microM), but elevated levels were found in 14 out of the 25 alcoholics. Alcoholics with elevated blood acetaldehyde showed a significantly higher ethanol metabolic rate than alcoholics with undetectable acetaldehyde (120 +/- 17 mg/kg/hr vs 104 +/- 11 mg/kg/hr, p < 0.02), but no differences were observed in the activities of alcohol and aldehyde dehydrogenases. Peak blood acetaldehyde levels were directly related to the ethanol metabolic rate (r = 0.48, p < 0.02), but not to activities of hepatic alcohol or aldehyde dehydrogenases. These results indicate that in chronic alcoholics the main determinant of the ethanol metabolic rate is hepatic function, while the rise of blood acetaldehyde is mainly dependent on the ethanol metabolic rate. Alcohol and aldehyde dehydrogenase activities do not seem to be rate-limiting factors in the oxidation of ethanol or acetaldehyde.

Acetaldehyde↗
PubMed1992

Class IV alcohol dehydrogenase (the gastric enzyme). Structural analysis of human sigma sigma-ADH reveals class IV to be variable and confirms the presence of a fifth mammalian alcohol dehydrogenase class.

Human gastric alcohol dehydrogenase (sigma sigma-ADH) was submitted to peptide analysis at picomole scale. A total of 72 positions were determined in the protein chain, providing information on three aspects of alcohol dehydrogenase structures in general. First, the data establish the presence of a unique class of the enzyme, now confirmed as class IV, expressed in gastric tissue and separate from another novel class, now termed class V. Second, the class IV gastric enzyme has active site relationships compatible with an ethanol-active, zinc-containing alcohol dehydrogenase. Third, this enzyme class is of the variable type, like that for the 'variable', classical liver alcohol dehydrogenase of class I, and in contrast to that for the 'constant' class III enzyme. Known human alcohol dehydrogenase structures now prove the presence of at least seven human genes for the enzyme and nine for the whole protein family.

Alcohol Dehydrogenase↗
PubMed1992

Alcohol dehydrogenase isoenzymes in rat development. Effect of maternal ethanol consumption.

The alcohol dehydrogenase (ADH) isoenzymes (alcohol:NAD oxidoreductase, EC 1.1.1.1) of classes I, III and IV were investigated by activity and starch gel electrophoresis analyses during rat ontogeny. Class I was studied in the liver, class III in the brain and class IV in the stomach and eyes. Classes I and IV exhibited very low activity during the fetal period, reaching 12% and 3%, respectively, of the adult value at birth. Class III was relatively more active in the fetus, with 38% of the adult activity at birth. In the three cases, activity increased after birth and adult values were found around day 20 (classes I and III), day 39 (stomach class IV) and after day 91 (eye class IV). The very low activity of the isoenzymes responsible for ethanol oxidation, i.e. liver class I and stomach class IV, in the fetus demonstrates that metabolism of ethanol during gestation is essentially performed by the maternal tissues. Development of ADH isoenzymes were also studied in the offspring of rats exposed to an alcoholic liquid diet. Activities of liver class I and stomach class IV were severely reduced: they were only 30% and 50%, respectively, of the control values. In contrast, eye class IV activity did not change and brain class III showed a 30% increase. Moreover, the concentration of liver soluble protein exhibited a 1.3-1.5-fold increase with respect to control animals. The effects on activities and liver protein were more pronounced in the adult than in the perinatal period, and they seem irreversible since normal values were not recovered after 6 weeks of feeding with a non-alcoholic diet. The low activities of the alcohol-oxidizing isoenzymes indicate tht maternal ethanol consumption results in an impaired ethanol metabolism of the offspring.

Alcohol Dehydrogenase↗
PubMed1991

Amphibian alcohol dehydrogenase, the major frog liver enzyme. Relationships to other forms and assessment of an early gene duplication separating vertebrate class I and class III alcohol dehydrogenases.

Submammalian alcohol dehydrogenase structures can be used to evaluate the origins and functions of the different types of the mammalian enzyme. Two avian forms were recently reported, and we now define the major amphibian alcohol dehydrogenase. The enzyme from the liver of the Green frog Rana perezi was purified, carboxymethylated, and submitted to amino acid sequence determination by peptide analysis of six different digests. The protein has a 375-residue subunit and is a class I alcohol dehydrogenase, bridging the gap toward the original separation of the classes that are observable in the human alcohol dehydrogenase system. In relation to the human class I enzyme, the amphibian protein has residue identities exactly halfway (68%) between those for the corresponding avian enzyme (74%) and the human class III enzyme (62%), suggesting an origin of the alcohol dehydrogenase classes very early in or close to the evolution of the vertebrate line. This conclusion suggests that these enzyme classes are more universal among animals than previously realized and constitutes the first real assessment of the origin of the duplications leading to the alcohol dehydrogenase classes. Functionally, the amphibian enzyme exhibits properties typical for class I but has an unusually low Km for ethanol (0.09 mM) and Ki for pyrazole (0.15 microM) at pH 10.0. This correlates with a strictly hydrophobic substrate pocket and one amino acid difference toward the human class I enzyme at the inner part of the pocket. Coenzyme binding is highly similar, while subunit-interacting residues, as in other alcohol dehydrogenases, exhibit several differences.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol Dehydrogenase↗