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X Parés

Publications and source records attributed to X Parés.

At least 19 recordsLinked to original sources
PubMed1998

Retinoids, omega-hydroxyfatty acids and cytotoxic aldehydes as physiological substrates, and H2-receptor antagonists as pharmacological inhibitors, of human class IV alcohol dehydrogenase.

Kinetic constants of human class IV alcohol dehydrogenase (sigmasigma-ADH) support a role of the enzyme in retinoid metabolism, fatty acid omega-oxidation, and elimination of cytotoxic aldehydes produced by lipid peroxidation. Class IV is the human ADH form most efficient in the reduction of 4-hydroxynonenal (k(cat)/Km: 39,500 mM(-1) min(-1)). Class IV shows high activity with all-trans-retinol and 9-cis-retinol, while 13-cis-retinol is not a substrate but an inhibitor. Both all-trans-retinoic and 13-cis-retinoic acids are potent competitive inhibitors of retinol oxidation (Ki: 3-10 microM) which can be a basis for the regulation of the retinoic acid generation and of the pharmacological actions of the 13-cis-isomer. The inhibition of class IV retinol oxidation by ethanol (Ki: 6-10 mM) may be the origin of toxic and teratogenic effects of ethanol. H2-receptor antagonists are poor inhibitors of human and rat classes I and IV (Ki > 0.3 mM) suggesting a small interference in ethanol metabolism at the pharmacological doses of these common drugs.

Alcohol Dehydrogenase↗
PubMed1998

First pass metabolism of ethanol is strikingly influenced by the speed of gastric emptying.

BACKGROUND: Ethanol undergoes a first pass metabolism (FPM) in the stomach and liver. Gastric FPM of ethanol primarily depends on the activity of gastric alcohol dehydrogenase (ADH). In addition, the speed of gastric emptying (GE) may modulate both gastric and hepatic FPM of ethanol. AIMS: To study the effect of modulation of GE on FPM of ethanol in the stomach and liver. METHODS: Sixteen volunteers (eight men and eight women) received ethanol (0.225 g/kg body weight) orally and intravenously, and the areas under the ethanol concentration time curves were determined to calculate FPM of ethanol. In seven of these subjects, FPM of ethanol was measured after the intravenous administration of 10 mg metoclopramide (MCP) and 20 mg N-butylscopolamine (NBS) in separate experiments to either accelerate or delay GE. GE was monitored sonographically by integration of the antral area of the stomach every five minutes for 90 minutes after oral ethanol intake. In addition, gastric biopsy specimens were taken to determine ADH activity and phenotype, as well as to evaluate gastric histology. Blood was also drawn for ADH genotyping. RESULTS: GE time was significantly delayed by the administration of NBS as compared with controls (p<0.0001) and as compared with the administration of MCP (p<0.0001). This was associated with a significantly enhanced FPM of ethanol with NBS compared with MCP (p = 0.0004). A significant correlation was noted between GE time and FPM of ethanol (r = 0.43, p = 0.0407). Gastric ADH activity did not significantly correlate with FPM of ethanol. CONCLUSION: FPM of ethanol is strikingly modulated by the speed of GE. Delayed GE increases the time of exposure of ethanol to gastric ADH and may therefore increase gastric FPM of ethanol. In addition, hepatic FPM of ethanol may also be enhanced as the result of slower absorption of ethanol from the small intestine. Thus a knowledge of GE time is a major prerequisite for studying FPM of ethanol in humans.

Administration, Oral↗
PubMed1997

Alcohol dehydrogenase of human and rat blood vessels. Role in ethanol metabolism.

Alcohol dehydrogenase (ADH) activity has been detected in all arteries and veins examined from humans and rat. In distinct human autopsy vessels, activity values range from 0.9 +/- 0.2 to 9.9 +/- 7.7 mU/mg. Distribution of the activity in human aorta was: intima (23.5%), media (74%) and adventia (2.5%). In most of the samples the beta1 beta1 isozyme of class I ADH was the only form responsible for the ADH activity. Class IV ADH (sigma sigma-ADH) was present in three of the 28 individuals examined. The rat blood vessels showed class IV, but not class I, ADH localized in endothelium and media. The physiological role of vascular ADH is probably related to retinoid metabolism and elimination of lipid peroxidation aldehydes. A contribution to human ethanol metabolism is supported by the significant amount of low-Km activity and the extension of the vascular system.

Adult↗
PubMed1996

Arabidopsis formaldehyde dehydrogenase. Molecular properties of plant class III alcohol dehydrogenase provide further insights into the origins, structure and function of plant class p and liver class I alcohol dehydrogenases.

A glutathione-dependent formaldehyde dehydrogenase (class III alcohol dehydrogenase) has been characterized from Arabidopsis thaliana. This plant enzyme exhibits kinetic and molecular properties in common with the class III forms from mammals, with a K(m) for S-hydroxymethylglutathione of 1.4 microM, an anodic electrophoretic mobility (pI: 5.3-5.6) and a cross-reaction with anti-(rat class III alcohol dehydrogenase) antibodies. The enzyme structure, deduced from the cDNA sequence, fits into the complex system of alcohol dehydrogenases and shows that all life forms share the class III protein type. The corresponding mRNA is 1.4 kb and present in all plant organs; a single copy of the gene is found in the genome. The class III structural variability is different from that of the ethanol-active enzyme types in both vertebrates (class I) and plants (class P), although class P conserves more of the class III properties than class I does. Also the enzymatic properties differ between the two ethanol-active classes. Active-site variability and exchanges at essential residues (Leu/Gly57, Asp/Arg115) may explain the distinct kinetics. These patterns are consistent with two different metabolic roles for the ethanol-active enzymes, a more constant function, reduction of acetaldehyde during hypoxia, for class P, and a more variable function, the detoxication of alcohols and participation in metabolic conversions, for class I. A sequence motif, Pro-Xaa-Ile/Val-Xaa-Gly-His-Glu-Xaa-Xaa-Gly, common to all medium-chain alcohol dehydrogenases is defined.

Alcohol Dehydrogenase↗
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↗