PubMed Health⌕ Search

Biomedical subjects

X Parés

Publications and source records attributed to X Parés.

At least 55 records · Page 3Linked to original sources
PubMed1991

Purification and characterization of a new alcohol dehydrogenase from human stomach.

Starch gel electrophoresis of homogenates from human stomach mucosa resolves three alcohol dehydrogenase (ADH) forms: the anodic chi-ADH (class III), the cathodic gamma-ADH (class I), and a new form of slow cathodic mobility that has not been previously characterized. In this work, we describe the purification in three chromatographic steps and the physical and kinetic characterization of this new human alcohol dehydrogenase, which we have named sigma-ADH. The enzyme exhibits the general physicochemical features (Mr, zinc content, subunit Mr, cofactor preference) of all mammalian alcohol dehydrogenases. The kinetic studies show a high Km value (41 mM) and a high kcat value (280 min-1) for ethanol at pH 7.5. The Km decreases as the alcohol increases its chain length. The aldehydes are better substrates than the corresponding alcohols, with m-nitrobenzaldehyde being the best substrate examined. sigma-ADH is strongly inhibited by 4-methylpyrazole, but with a Ki (10 microM) still higher than that for a class I isoenzyme. These properties suggest that sigma-ADH is a class II isoenzyme, different from pi-ADH and similar to that previously described by us in rat stomach. At the high ethanol concentrations in stomach after drinking, sigma-ADH is probably the ADH form with the largest contribution to human gastric ethanol metabolism.

Alcohol Dehydrogenase↗
PubMed1991

Structure and function of ribonuclease A binding subsites.

Ribonuclease A binds nucleic acids through multiple electrostatic interactions between the phosphates of the polynucleotide and the positive groups (side chains of lysines and arginines) of the protein subsites. The bases only play a significant role in the binding at the active site. The active centre p1R1B1 sites determine the specificity of the catalytic cleavage. The phosphate-binding subsites p2 (Lys-7 and Arg-10), p1 (Lys-41, His-12 and His-119) and p0 (Lys-66) are essential for an effective catalysis and are conserved in all mammalian pancreatic ribonucleases. Additional phosphate-binding subsites confer further catalytic efficiency, probably by avoiding non-productive binding. The minimum chain size for optimum catalysis is probably longer than six or seven nucleotides. The full occupancy of binding sites by the long chain polynucleotides would explain the preference of the enzyme for these substrates. The multiplicity of binding subsites is responsible for the helix-destabilizing activity of ribonuclease A. Its capacity for destroying the secondary structure of single-stranded nucleic acids may be of importance for the complete hydrolysis of RNA in the digestive tract. A large variety of proteins, with very different structures and functions, interact with nucleic acids. An analysis of their binding properties shows that there is no general model for protein-nucleic acid interaction. However, the vast amount of work on the ribonuclease A binding subsites should serve as a model for the study of the binding properties of many other proteins that recognize nucleic acids.

Animals↗
PubMed1990

Class IV mammalian alcohol dehydrogenase. Structural data of the rat stomach enzyme reveal a new class well separated from those already characterized.

The stomach form of alcohol dehydrogenase has been structurally evaluated by peptide analysis covering six separate regions of the rat enzyme. Overall, this new structure differs widely (32-40% residue differences) from the structures of three classes of alcohol dehydrogenase characterized before from the same species. Consequently, this novel enzyme constitutes a true fourth class of mammalian alcohol dehydrogenase. In particular, differences are extensive also towards class II, although enzymatic and physicochemical properties initially suggested overall similarities with class II. The new structure establishes the presence of one further alcohol dehydrogenase mammalian gene, extends the enzyme family derived from repeated gene duplications, and confirms tissue-specific expressions.

Alcohol Dehydrogenase↗
PubMed1990

Fast atom bombardment mass spectrometry and chemical analysis in determinations of acyl-blocked protein structures.

Peptide generation and fast atom bombardment mass spectrometry in combination with conventional chemical analysis was used to identify the blocking group and establish the N-terminal structure of six different proteins at the nanomole level. In this manner, the first terminal structures of three non-mammalian alcohol dehydrogenases were determined, demonstrating the presence of N-terminal acetylation in these piscine, amphibian, and avian enzymes. Similarly, two different yeast glucose-6-phosphate dehydrogenases and a minor variant of a human alcohol dehydrogenase were found to be acetylated. The exact end location of C-terminal structures was also established. Together, the analyses permit the definition of terminal regions and blocking groups, thus facilitating the delineation of remaining structures.

Acetylation↗
PubMed1990

Chemical modification by pyridoxal 5'-phosphate and cyclohexane-1,2-dione indicates that Lys-7 and Arg-10 are involved in the p2 phosphate-binding subsite of bovine pancreatic ribonuclease A.

Steric and chemical evidence had previously shown that residues Lys-7 and/or Arg-10 of bovine pancreatic RNAase A could belong to the p2 phosphate-binding subsite, adjacent to the 3' side of the main site p1. In the present work chemical modification of the enzyme with pyridoxal 5'-phosphate and cyclohexane-1,2-dione was carried out in order to identify these residues positively as part of the p2 site. The reaction with pyridoxal 5'-phosphate yields three monosubstituted derivatives, at Lys-1, Lys-7 and Lys-41. A strong decrease in the yield of derivatives at Lys-7 and Lys-41 was observed when either p1 or p2 was specifically blocked by 5'-AMP or 3'-AMP respectively. These experiments indicate that both sites are needed for the reaction of pyridoxal 5'-phosphate with RNAase A to take place. The positive charge in one of the sites interacts with the phosphate group of pyridoxal 5'-phosphate, giving the proper orientation to the carbonyl group, which then reacts with the lysine residue present in the other site. The absence of reaction between pyridoxal 5'-phosphate and an RNAase derivative that has the p2 site blocked supports this hypothesis. Labelling of Lys-7 with pyridoxal 5'-phosphate has a more pronounced effect on the kinetics with RNA than with the smaller substrate 2',3'-cyclic CMP. In addition, when the phosphate moiety of the 5'-phosphopyridoxyl group was removed with alkaline phosphatase the kinetic constants with 2',3'-cyclic CMP returned to values very similar to those of the native enzyme, whereas a higher Km and lower Vmax. were still observed for RNA. This indicates that this new derivative has recovered a free p1 site and, hence, the capability to act on 2',3'-cyclic CMP, but the presence of the pyridoxyl group bound to Lys-7 is still blocking a secondary phosphate-binding site, namely p2. Finally, reaction of cyclohexane-1,2-dione at Arg-10 is suppressed in the presence of 3'-AMP but only a 19% decrease is observed with 5'-AMP, suggesting that Arg-10 is also close to the p2 phosphate-binding subsite.

Animals↗
PubMed1989

Role of extrahepatic alcohol dehydrogenase in rat ethanol metabolism.

Rat alcohol dehydrogenase exhibits three isoenzymes with very different capacities of ethanol oxidation and with characteristic distribution in tissues. ADH-1 (class II isoenzyme, Km = 5 M) is especially concentrated in the most external organs: auditive, bucal, and nasal mucoses, cornea, esophagus, stomach, rectum, penis, and vagina. ADH-2 (class III isoenzyme) is present in all organs but has a poor activity with ethanol. ADH-3 (class I isoenzyme, Km = 1.4 mM) is the main liver isoenzyme, also present in lung, intestine, kidney, and sexual organs. At 33 mM ethanol and pH 7.5, total hepatic activity (3.5 +/- 0.6 units) represents 90% of the whole activity in the male rat, while the remaining 10% is distributed in many organs. The skin is the extrahepatic organ with the highest total activity (88 +/- 15 mU) followed by testis and small intestine. ADH-3 accounts for 96% of total activity (90% hepatic and 6% extrahepatic) and ADH-1 contributes with 4% (extrahepatic). However, in conditions that may be found in the digestive tract mucose after ethanol ingestion (pH 7.5, 1 M ethanol), stomach and small intestine activities represent 10% of the liver activity at 33 mM ethanol. Therefore, oral administration of ethanol will result in a higher contribution of the extrahepatic activity than will intravenous or intraperitoneal administration, because of the great ADH-1 content of the digestive tract. On the other hand, pyrazole inhibition constants at pH 7.5 for ADH-1 (33 mM) and ADH-3 (4.2 microM) are much higher than those at pH 10.0 (0.56 mM and 0.4 microM) and indicate that at the usual concentration of inhibitor only ADH-3 activity will be effectively suppressed. ADH-1 will be, therefore, responsible in part for the residual ethanol oxidation activity in pyrazole-treated rats.

Alcohol Dehydrogenase↗
PubMed1989

Influence of liver disease on hepatic alcohol and aldehyde dehydrogenases.

The hepatic activities and the isoenzyme patterns of both alcohol dehydrogenase and aldehyde dehydrogenase have been studied in 60 alcoholics with varying degrees of liver damage (from normal tissue or minimal changes to cirrhosis with alcoholic hepatitis) and in 24 nonalcoholics with chronic hepatitis or cirrhosis in order to ascertain their association with liver damage. In alcoholics both alcohol dehydrogenase and low-Km aldehyde dehydrogenase activities decreased proportionally with the severity of liver disease. In contrast, in nonalcoholics, there was a reduction of low-Km aldehyde dehydrogenase activity related to the severity of liver injury, but alcohol dehydrogenase was similar in patients with chronic hepatitis and nonalcoholic cirrhosis. There were no significant changes in total and high-Km aldehyde dehydrogenase activities among the different histologic groups studied, although the lowest activities were observed in patients with more severe liver injury. The prevalence of atypical alcohol dehydrogenase was similar in alcoholic (6.6%) and in nonalcoholic (8.3%) liver disease. All patients exhibited isoenzyme aldehyde dehydrogenase II, whereas isoenzyme I was not detected in 39.5% of the alcoholic patients and in 9.5% of those with nonalcoholic liver disease. The lack of aldehyde dehydrogenase I was observed in cases with the lowest enzymatic activities. These results suggest that the decrease of alcohol and aldehyde dehydrogenase activities in alcoholics is not a primary defect and, therefore, their decrease is secondary to liver damage. It is speculated that the diminution of alcohol dehydrogenase, found particularly in alcoholics, could be due to centrilobular cell necrosis.

Alcohol Dehydrogenase↗
PubMed1989

Chemical and computer graphics studies on the topography of the ribonuclease A active site cleft. A model of the enzyme-pentanucleotide substrate complex.

The affinity labelling of bovine pancreatic ribonuclease A with 6-chloropurine 5' ribonucleotide allowed us to postulate the existence of a new phosphate-binding subsite, P2, adjacent to the main purine-binding subsite. The study of this reaction in greater detail together with the study of a complex of the enzyme with the pentanucleotide pApUpApApG by means of model building and computer graphics indicate that at least five phosphate groups of the RNA molecule can interact with five positive regions of the enzyme. In each one a lysine residue is present: Lys-104, -66, -41, -7 and -37 appear sequentially in the 5'----3' direction. The distance between each lysine is 0.7-0.8 nm, the same distance as that found between the phosphate groups on the RNA molecule. The study also enabled many amino acid residues of the enzyme to be described as forming part of, or being near, the different binding subsites.

Binding Sites↗
PubMed1988

Aldehyde oxidation in human placenta. Purification and properties of 1-pyrroline-5-carboxylate dehydrogenase.

The human placenta contains a considerable amount of 1-pyrroline-5-carboxylate dehydrogenase (23 +/- 6 micrograms/g; n = 12), about 25% of the concentration present in liver. The enzyme is the only form in placenta that oxidizes short- and medium-chain aldehydes, which facilitates its purification from this organ. It can be purified to homogeneity by successive chromatographies on DEAE-cellulose, 5'-AMP-Sepharose and Sephacryl S-300. From 500 g of tissue, about 2.1 units of enzyme can be obtained with a 12% yield. Placental 1-pyrroline-5-carboxylate dehydrogenase is a dimer of Mr-63,000 subunits. It exhibits a pI of 6.80-6.65, and is specific for 1-pyrroline-5-carboxylate, the cyclic form of glutamate gamma-semialdehyde (Km = 0.17 mM, kcat. = 870 min-1), although it also oxidizes short-chain aliphatic aldehydes such as propionaldehyde (Km = 24 mM, kcat. = 500 min-1). These properties are very close to those of the liver enzyme, indicating a strong similarity between the enzyme forms from both organs. The enzyme is highly sensitive to temperature, showing 50% inhibition after incubation for 0.8 min at 45 degrees C or after 23 min at 25 degrees C. It is irreversibly inhibited by disulfiram, and a molar ratio inhibitor: enzyme of 60:1 produced 50% inhibition after incubation for 10 min. A subcellular-distribution study indicates that the enzyme is located in two compartments: the mitochondria, with 60% of the total activity, and the cytosol, with 40% activity. The physiological role of the enzyme in placental amino acid metabolism is discussed.

1-Pyrroline-5-Carboxylate Dehydrogenase↗
PubMed1988

Nucleotide binding and affinity labelling support the existence of the phosphate-binding subsite p2 in bovine pancreatic ribonuclease A.

When the reaction of bovine pancreatic ribonuclease A with 6-chloropurine riboside 5'-monophosphate was carried out in the presence of several natural mononucleotides, a decrease of 25-75% was found in the amount of the reaction product derivative II (the main product of the reaction which has the nucleotide label at the alpha-NH2 group of Lys-1). The efficiency of inhibition followed the order 3'-AMP greater than 5'CMP approximately equal to 5'AMP greater than 3'CMP. Previous studies indicate that this order reflects the extent of occupancy of p2, a phosphate-binding subsite adjacent to the catalytic centre. This finding suggests that derivative II is the result of affinity labelling and that the phosphate group of the halogenated nucleotide binds to p2 before the reaction takes place. The dissociation constants and stoichiometry of the interaction between native enzyme, derivative II and derivative E (homologous to derivative II, but labelled with a nucleoside instead of a nucleotide) with 3'AMP and 5'AMP at several pH values were also determined. Although in general one strong binding site was found, no strong binding occurs between 3'AMP and derivative II. It is concluded that the phosphate of the label occupies the same site p2, as the phosphate of 3'AMP. Finally, the pH dependence for the binding of 3'AMP and 5'AMP to RNAase A indicates that they bind to different protein groups. The results presented support the structure of the active site of ribonuclease A postulated previously (Parés, X., Llorens, R., Arús, C. and Cuchillo, C.M. (1980) Eur. J. Biochem. 105, 571-579).

Adenosine Monophosphate↗
PubMed1987

Acetylated N-terminal structures of class III alcohol dehydrogenases. Differences among the three enzyme classes.

The protein chains of mammalian alcohol dehydrogenases typically lack free alpha-amino groups. The blocked N-terminal regions of the class III type of the rat (ADH-2), human (chi chi) and horse enzymes were isolated by digestions with proteases, and characterized by mass-spectrometry supplemented with chemical analysis of the peptides and their redigestion fragments. Results were confirmed by synthesis of the corresponding peptides, followed by chromatographic comparisons of the native and synthetic products. The N-terminal regions of the three class III alcohol dehydrogenase subunits are homologous but differ from the class I and II enzymes in both the exact start position and the amino acid sequence, which suggests that different N-terminal structures are typical for each of the three classes.

Acetylation↗
PubMed1987

Characterization of three isoenzymes of rat alcohol dehydrogenase. Tissue distribution and physical and enzymatic properties.

Rat tissues contain three different isoenzymes of alcohol dehydrogenase (ADH) that we have named ADH-1, ADH-2 and ADH-3, ADH-1 is an anodic isoenzyme present in high amounts in the ocular tissues, stomach and lung. ADH-2 is also anodic and has been found in all the rat organs examined. ADH-3 is the group of cathodic ADH forms, mainly present in liver, that has been the subject of the majority of the previous studies on rat ADH. The three isoenzymes have been purified to homogeneity and characterized. All of them have similar physical characteristics: Mr 80,000, with two subunits of Mr 40,000; they contain four atoms of Zn per molecule, and prefer NAD+ as cofactor. Isoelectric points are, however, different: 5.1 for ADH-1, 5.95-6.3 for ADH-2 and 8.25-8.4 for ADH-3. ADH-3 exhibits a Km for ethanol of 1.4 mM, a broad substrate specificity and is strongly inhibited by pyrazole (Ki = 0.4 microM). ADH-2 shows substrate specificity toward long-chain alcohols and aldehydes, cannot be saturated by ethanol and is practically insensitive to pyrazole (Ki = 78.4 mM). ADH-1 has intermediate properties, with a Km for ethanol of 340 mM, a broad substrate specificity and Ki for pyrazole of 0.56 mM. Rat ADH-1, ADH-2 and ADH-3 exhibit many analogies with human ADH classes II, III and I respectively. The specific localization and kinetic properties of rat ADH isoenzymes suggest that ADH-1 and ADH-3 may act as metabolic barriers to external alcohols and aldehydes whereas ADH-2 may have a function in the metabolism of the endogenous long-chain alcohols and aldehydes.

Alcohol Dehydrogenase↗
PubMed1987

Mammalian alcohol dehydrogenase: characteristics of class III isoenzymes.

The kinetic characteristics of alcohol dehydrogenase class III have been studied using class III isoenzymes purified from human liver (X-ADH) and rat liver (ADH-2). Our results confirm that long chain primary alcohols and aldehydes are the best substrates, although some aromatic compounds can also be actively metabolized. Kinetic analysis suggests an ordered bibi mechanism for X-ADH. Ethanol can be oxidized by class III isoenzymes at high substrate concentration, but with a very slow rate. Thus, their contribution to physiological ethanol elimination is probably insignificant. The general properties of the class III isoenzymes isolated from different mammals by ourselves and other authors are discussed.

Alcohol Dehydrogenase↗
PubMed1987

Hepatic alcohol and aldehyde dehydrogenases in liver disease.

To investigate the influence of liver injury on the activities of hepatic alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), these enzymes have been measured in tissue from alcoholic and non alcoholic patients with different severity of liver damage. ADH and ALDH activities decreased proportionatelly with the progression of liver disease in alcoholics. By contrast, in non-alcoholics, there was a reduction of Low-Km ALDH related with the severity of liver injury but ADH was similar in patients with chronic hepatitis and non-alcoholic cirrhosis. Furthermore, ADH was significantly lower in alcoholic than in non-alcoholic cirrhotics. These results suggests that the decreased ADH and ALDH in alcoholics are not primary abnormalities predisposing to alcoholism and alcoholic liver disease. The diminution of ADH found only in alcoholics could be due to the loss of the enzyme produced by centrolobulillar cell necrosis, that is often observed in alcoholic liver disease.

Adult↗
PubMed1986

Ocular alcohol dehydrogenase in the rat: regional distribution and kinetics of the ADH-1 isoenzyme with retinol and retinal.

Starch-gel electrophoresis of rat ocular tissues shows two anodic isoenzymes of alcohol dehydrogenase (ADH), designated as ADH-1 and ADH-2, ADH-1 is characteristic of the ocular tissues, and corresponds to more than 95% of all ADH activity in the eye. The well known cathodic forms of rat liver ADH, that we named ADH-3, are not observed in the ocular tissues. ADH-1 is detected in retina, pigment epithelium-choroid, ocular fluid, and cornea but not in the lens. The cornea exhibits the highest ADH activity [200 +/- 59 milliunits (munits) mg-1] followed by the pigment epithelium-choroid (11 +/- 7 munits mg-1). Activity in the retina is very small (0.6 +/- 0.2 munit mg-1) and represents only 0.6% of the total activity in the eye. Most of the rat ocular ADH is localized in the cornea (68%) where it could play a significant role in the detoxication of the alcohols of a broad range of structures. Purified ADH-1 shows a low Km for retinol oxidation (20 microM) and for retinal reduction (30 microM) indicating that this isoenzyme may have a function in the metabolism of retinoids. Ethanol competitively inhibits retinol oxidation, but with a very high apparent inhibition constant (0.6 M) demonstrating that the inhibitory effect is not significantly at the usual concentrations found in the blood during ethanol intoxication.

Alcohol Dehydrogenase↗
PubMed1984

Physical and enzymatic properties of a class III isozyme of human liver alcohol dehydrogenase: chi-ADH.

chi-Alcohol dehydrogenase (chi-ADH), a class III isozyme characterized by its anodic electrophoretic mobility and lack of inhibition by 4-methylpyrazole, has been isolated from human liver and purified to homogeneity in a reducing medium. chi-ADH resembles other human liver ADH isozymes of classes I and II with respect to its molecular weight, dimeric structure, stoichiometry of zinc and NADH binding, and pH optima for the oxidation of alcohols. This homodimer exhibits subtle differences in its absorption spectrum and amino acid composition relative to those of other human isozymes but differs markedly from their specificity toward alcohols and aldehydes. chi-ADH oxidizes ethanol very poorly. The reaction is bimolecular, and an apparent Km cannot be discerned up to 2.3 M ethanol. The enzyme is inactive toward methanol, ethylene glycol, digitoxigenin, digoxigenin, and gitoxigenin , but alcohols with carbon chain lengths greater than four are oxidized rapidly with Km values decreasing with increasing carbon chain length. Taken jointly, the composition, structure, and enzymatic properties of the ADH isozymes purified and studied so far strongly imply that their metabolic roles, yet to be discovered, will give a new perspective to ethanol metabolism and pathology.

Alcohol Dehydrogenase↗