PubMed Health⌕ Search

Biomedical subjects

A Cortés

Publications and source records attributed to A Cortés.

At least 19 recordsLinked to original sources
PubMed1992

Kinetic studies of the regulation of mitochondrial malate dehydrogenase by citrate.

Mitochondrial malate dehydrogenase shows a complex regulation pattern in the presence of citrate. Previously published results indicate that this enzyme is activated by citrate in the NAD(+)----NADH direction and inhibited in the opposite direction. Moreover, high concentrations of L-malate or oxaloacetate produce deviations from the Michaelis-Menten behaviour. Results reported in this paper clearly show that citrate both activates and inhibits mitochondrial malate dehydrogenase in the same direction (NAD(+)----NADH), and in the same reaction medium, depending on substrate concentration. This surprising effect has made it necessary to propose a new kinetic mechanism that extends those previously suggested and allows us to explain both the citrate effect (activating or inhibitory) and the effect of high concentrations of L-malate and oxaloacetate.

Animals↗
PubMed1991

Heterogeneity of chicken liver cytosolic aspartate aminotransferase.

The isolated native molecular forms of chicken liver cytosolic aspartate aminotransferase give rise to two kinds of generation processes: (a) on storage, molecular forms are transformed into a series of variants with increasing anodic mobilities; and (b) addition of thiol reagents not only avoids the process, but causes the partial transformation of minor subforms into variants with higher isoelectric point values. In both cases the mobilities of each generated variant coincide with that of the corresponding native molecular form. The variants generated either by storage or in the presence of thiol reagents were separated by chromatofocusing. Several comparative studies have demonstrated the structural and functional identity between native molecular forms and 'in vitro' active generated variants of the enzyme. The results obtained suggest that native minor subforms arise from the major alpha form due to oxidation process and might represent intermediate species in the intracellular cytosolic aspartate aminotransferase turnover.

Animals↗
PubMed1991

Heterogeneity of human liver alanine aminotransferase due to sulfhydryl groups oxidation.

The cytosolic isoenzyme of human liver alanine aminotransferase exhibited a progressive change in its chromatographic behavior on DEAE-Sepharose when partially purified preparations were stored for up to 8 days at 4 degrees C. This change was characterized by the appearance of an additional chromatographic variant and was avoided by addition of 2-mercaptoethanol. The experimental evidence presented indicates that the progressive oxidation of free sulfhydryl groups of the enzyme is responsible for the charge modifications and heterogeneity observed.

Alanine Transaminase↗
PubMed1990

[Response to recombinant DNA antihepatitis B vaccine in mentally retarded patients with Down's syndrome. A controlled study].

To investigate the response of mentally retarded individuals (MR) with Down's syndrome (Down-MR) to recombinant hepatitis B vaccine, three doses (20 micrograms per dose) were administered on the usual schedule (months 0, 1 and 6) to two groups of MR with mean age of 14.6 years. The first group consisted of 32 MR-Down. The second group consisted of 35 MR other etiologies (non Down-MR). Both had the same sex distribution and similar ages and weight/height index. The post vaccination anti-HBs titers were measured on months 1, 2, 6 and 8. The results could be analysed in 63 MR. Eight months after vaccination, 100% of Down-MR and 91% of non Down-MR developed a response to the vaccine (anti-HBs greater than 10 IU/l). Both groups achieved high antibody titers (geometric mean 4.298 and 6.424, respectively). A significant inverse correlation of anti-HBs with age was found, but not with sex of with the weight-height index. It was concluded that Down-MR in young age have a normal response to recombinant hepatitis B vaccine at the usual dose and schedule. Therefore, the goal to suppress the reservoir of hepatitis B in Down-MR both in institutions for MR and in normal schools should be achieved.

Adolescent↗
PubMed1990

[Treatment of macroprolactinomas with delayed bromocriptine. Effectiveness of a single intramuscular injection].

The aim of the present study was to evaluate the effectiveness and tolerance of a new pharmaceutical preparation of long acting bromocryptine (bromocryptine depot of L.A.), characterized by the slow release of bromocryptine during 4 or 6 weeks after a deep intramuscular injection. It was administered to 9 patients with macroprolactinoma, 7 of which had visual abnormalities. The tolerance of the drug was excellent, and only one patient had nausea within the first 24 hours. In all cases, PRL values fell between 40% and 97%. All patients with visual abnormalities, including 2 patients with cranial nerve palsy (IIIth and VIIth pairs) returned to normal or improved. In the CT controls carried out after 4 weeks of therapy a reduction in tumor size was observed in 7 of 9 patients. Two patients were operated through the transesphenoidal route, PRL being demonstrated in the immunohistochemical study of the resected specimen. Subsequently, all patients received oral bromocryptine therapy with perfect tolerance. The results show that parenteral long acting bromocryptine is an effective, well tolerated and convenient way to start the therapy of macroprolactinoma, even when severe visual abnormalities are present.

Adolescent↗
PubMed1990

Comparative analysis of the reduction of oxaloacetate by human hepatoma and normal liver extracts.

An apparent activation of the malate dehydrogenase activity is observed in the double-reciprocal plot at high oxaloacetate concentrations when human hepatoma extracts are analyzed. This phenomenon does not occur in healthy liver samples. In hepatoma extracts, the ratio of lactate dehydrogenase to malate dehydrogenase activities becomes five-fold higher than that of normal liver. Experiments performed with mixtures of both purified enzymes and, conversely, by using oxamate, a specific inhibitor of lactate dehydrogenase, reveal that the deviation in Michaelis-Menten behavior observed is due to the oxaloacetate reductase activity of lactate dehydrogenase instead of the presence of a novel malate dehydrogenase isoenzyme.

Carcinoma, Hepatocellular↗
PubMed1990

Kinetic formulations for the reduction of ketomalonate by lactate dehydrogenase.

Initial rate kinetic studies of lactate dehydrogenase with ketomalonate and NADH as substrates suggest that this enzymatic system is adapted to a rapid equilibrium ordered bi-bi ternary complex mechanism. The application of the reaction product inhibition method reveals the existence of the enzyme-NADH-hydroxymalonate and enzyme-NAD(+)-ketomalonate abortive complexes. This kinetic behaviour is confirmed by the differential inhibition induced by several alternate products on the pyruvate-lactate dehydrogenase-NADH and ketomalonate-lactate dehydrogenase-NADH systems.

Animals↗
PubMed1990

A rapid procedure for eliminating chromatofocusing buffer and concentrating minor active subforms of mitochondrial malate dehydrogenase.

Mitochondrial malate dehydrogenase from several sources contains different molecular forms whose origin is still under discussion. Separation of these subforms has been achieved by chromatofocusing. A simple and rapid method, based on 5' AMP Sepharose chromatography, has been developed to concentrate mitochondrial malate dehydrogenase subforms and simultaneously remove chromatofocusing buffer.

Animals↗
PubMed1990

Factors affecting L-malate activation of mitochondrial malate dehydrogenase from chicken liver.

Mitochondrial malate dehydrogenase is activated by high concentrations of L-malate. In this paper, several factors affecting this activation on chicken liver enzyme have been investigated. The results obtained show clearly that this phenomenon is an intrinsic property of this enzyme since it does not depend on pH or ionic strength of the reaction medium. However, L-malate activation decreases when NAD+ concentration diminishes (5mM----0.2 mM) in such a way that when NAD+ concentration is 0.2 mM, L-malate does not activate mitochondrial malate dehydrogenase. On the other hand, several activators of this enzymatic system, such as citrate or phosphate, also produce the elimination of this activation by L-malate; in this case, the phenomenon seems be due to a competitive binding to a regulatory site of the different metabolites implied.

Animals↗
PubMed1989

[Mentally deficient patients and infection caused by hepatitis B virus. Prevalence in our area].

To assess the prevalence of hepatitis B virus (HBV) infection in medium level mentally impaired patients (MIP), 620 MIP were evaluated; 181 of them had Down's syndrome and were active inmated of open institutions. At the time of the study, 28.7% had some positive serum marker of HBV infection, and 5.8% were virus carriers. The highest rate of seropositive individuals (48%) was found in male MIP with Down's syndrome. The rate of seropositive individuals was higher among those MIP who had attended special education centers than in those who had not. The tendency to remain as HBV carrier was higher in males with Down's syndrome. Our results confirm the need for prophylaxis in this population.

Adolescent↗
PubMed1989

Purification and characterization of chicken brain cytosolic aspartate aminotransferase.

Aspartate aminotransferase from the cytosolic fraction of chicken brain was isolated with acceptable yield and high degree of purity. The enzyme appeared in multiple molecular forms: alpha, beta, gamma, and delta (alpha predominates), as detected by polyacrylamide gel electrophoresis with specific staining. These different forms of the enzyme were separated by DEAE-Sephacel chromatography, and showed different isoelectric points and maximal velocities values, whereas their molecular weight, optimum pH and Michaelis constants were very similar. Generation process studies suggest that minors subforms of the enzyme could be raised from alpha form by a mechanism in which the oxidation of particular amino acid groups are involved.

Animals↗
PubMed1989

A field lab method to determine urine concentration in small mammals.

1. The concentrations of 136 urine samples from four species of small mammals were compared using osmometry, refractometry and a colorimetric test for urea concentration. 2. To obtain a wide range of concentrations (430-3950 mOsm/kg), urine samples were collected under normal and dehydration conditions. 3. Regression analyses of paired values indicate that measurements of total solids concentration (refractometric method) permit evaluations of urine osmolality and estimations of the concentration of urea with a high degree of confidence.

Animals↗
PubMed1989

Cytosolic aspartate aminotransferases from different chicken tissues: purification and characterization of their multiple forms.

Cytosolic aspartate aminotransferases from chicken heart, liver, spleen, skeletal muscle and breast muscle differed in number of their molecular forms, detected by polyacrylamide gel electrophoresis and specific staining. The number of molecular forms varied from tissue to tissue but the electrophoretic mobilities of a given form in all tissues were analogous. Within a single tissue most of the enzyme activity was present as the lowest-running band (alpha form) and the rest was distributed in minor bands termed (B,tau, alpha and epsilon forms). We report a method for the purification of cytosolic aspartate aminotransferases from various chicken tissues. The procedure can be carried out in one week and allows the obtention of isolated molecular forms of the enzyme, independently of the tissue under study. Separation of multiple forms was also achieved by chromatofocusing. The isoelectric points determined by this method for a given form in all five tissues were analogous and differed from those of the molecular forms of the enzyme from other origins. An Mr of 100,000 was obtained for all molecular forms of the five chicken tissues studied.

Animals↗
PubMed1988

Kinetic studies of chicken and turkey liver mitochondrial aspartate aminotransferase.

The kinetic behaviour of chicken liver and turkey liver aspartate aminotransferases (L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1) was studied. Steady-state data were obtained from a wide range of concentrations of substrates and product L-glutamate. The data were fitted by rational functions of degree 1:1, 1:2 and 2:2 with respect to substrates and 0:1, 1:1, 0:2 and 1:2 with regard to product (L-glutamate), by using a non-linear regression program that guarantees the fit. The goodness of fit was improved by the use of a computer program that combines model discrimination parameter refinement and sequential experimental design. It was concluded that aspartate aminotransferase requires a minimum velocity equation of degree 2:2 for L-aspartate, 2:2 for 2-oxoglutarate and 1:2 for L-glutamate. Finally, a plausible kinetic mechanism that justifies these experimental results is proposed.

Animals↗
PubMed1988

Generation process of cytosolic aspartate aminotransferase molecular forms by several treatments.

Alpha-, beta-, and gamma-forms of chicken liver cytosolic aspartate aminotransferase generate variants on storage (4 degrees C, 25 days). The variants developed from each isolated form appeared as evenly spaced bands with increasing anodic mobilities after polyacrylamide gel electrophoresis (PAGE), pH 8.8, and specific staining. Their mobilities coincided with those of the more negatively charged forms present in fresh tissue. Development of faster-running variants on storage was avoided by addition of thiol reagents to the freshly isolated forms. In their presence, beta- and gamma-forms were partially transformed into one and two variants with lower anodic mobilities analogous to those of native alpha- and beta-forms. Short pH and heat treatments did not modify the electrophoretic patterns of the alpha-, beta-, and gamma-forms, but the incubation with 5 mM L-ascorbic acid (37 degrees C, 7 h) produced more anodic active bands. The formation of these variants was inhibited by the presence, in the incubation mixture, of superoxide dismutase and catalase. The kinetic parameters of the forms submitted to the different treatments were similar to those of the freshly isolated subforms. The results obtained suggest that minor subforms of the enzyme could be generated in vivo by a mechanism in which the oxidation of particular amino acid groups is involved.

Animals↗
PubMed1988

Purification of malate dehydrogenase from chicken liver mitochondria. Existence of a small quantity of cytosolic isoenzyme.

1. A new purification method for chicken liver mitochondrial malate dehydrogenase is described. The application of affinity chromatography through 5'AMP-Sepharose and Blue-Sepharose permits to obtain homogeneous preparations, with good yields (47%), in a short time (48 hr). 2. The 5'AMP-Sepharose chromatography reveals the presence of two malate dehydrogenase species in the mitochondrial extracts. 3. A comparative study of these forms point out the cytosolic nature of the minority form and suggests that its presence could be due to a slight interaction of the cytosolic malate dehydrogenase with mitochondrial membranes.

Animals↗