Carlos Burgos

Inhibition by gossypol of oxidoreductases from Trypanosoma cruzi

The effects of gossypol, a polyphenolic compound isolated from the cotton plant upon six oxidoreductases from cultured epimastigotes of Typanosoma cruzi were studied. Gossypol was a powerful inhibitor of the alpha-hydroxyacid and malate dehydrogenases, NAD-linked enzymes, and of glutamate dehydrogenase, malic enzyme and glucose-6-phosphate dehydrogenase, NADP-dependent enzymes. The drug did not have an effect on succinate dehydrogenase, a flavoprotein. The Ki values with respect to substrate were 0.73, 0.3 and 3.5 microM for alpha-hydroxyacid, malate and glutamate dehydrogenases, respectively, and 1.1, 0.19 and 7.8 microM with respect to the coenzyme. Inhibition was noncompetitive with respect to substrate and uncompetitive in relation to the coenzyme.

Properties of α-hydroxyacid dehydrogenase isozymes from Trypanosoma cruzi

Whole cell extracts of culture epimastigotes of Trypanosoma cruzi (Tulahuen strain) have α-hydroxyacid dehydrogenase activity which catalyzes the NAD-linked reaction α-ketoacid ⇋ α-hydroxyacid, with a variety of substrates. Two molecular forms of the enzyme have been separated by means of gel electrophoresis. These isozymes were partially purified by DEAE-cellulose chromatography and ammonium sulfate precipitation. Molecular weights were estimated and some catalytic properties were determined with purified isozymes. The faster migrating fraction (isozyme I) has a molecular weight of 85 500 and showed significant activity against linear 3–5 carbon chain substrates. The lowest Km value was obtained for pyruvate. Isozyme II (MW 60 500) utilizes linear and branched chain substrates with 4–6 carbon atoms. Its highest activity and lowest Km value were recorded with α-keto-isocaproate as substrate.

A shuttle system for the transfer of reducing equivalents in mouse sperm mitochondria

Abstract Studies have been carried out on an in vitro reconstituted system composed of mouse lactate dehydrogenase isozyme X or C4, branched chain amino acid aminotransferase, NAD, alpha-hydroxy isocaproate, glutamate and mouse sperm mitochondria. This system demonstrated capacity for the oxidation of extramitochondrial NADH. It is proposed that a branched chain alpha-hydroxyacid / amino acid shuttle for the transfer of reducing equivalents from cytosol to mitochondria may be functional in mouse spermatozoa.

Correlation between muscular lactate dehydrogenase isoenzyme patterns and flight habits of bats

Abstract 1. 1. Electrophoretic patterns of lactate dehdyrogenase isoenzymes and ratios of lactate dehydrogenase activity at two concentrations of pyruvate (2·0 mM/0·2 mM) have been determined in extracts of pectoral and hind limb muscles of five species of bats. 2. 2. Aerodynamic characteristics and flight habits of these bats are described. 3. 3. There was a clear predominance of isoenzyme B 4 and lowest high/low substrate ratios in the pectoral muscle of those species capable of sustained flight. Larger proportions of isoenzyme A 4 and highest high/low substrate ratio were found in the hind limb muscle extract from a species in which the hind legs are not involved in flight activity. 4. 4. This correlation is in agreement with the functional role assigned to the A 4 and B 4 isoenzymes.

Effect of temperature upon inhibition by substrate of lactate dehydrogenase isoenzymes from a poikilotherm

The effect of temperature upon the inhibition by substrate (pyruvate and lactate) and the values of K1 for NAD+ and pyruvate have been studied comparatively on lactate dehydrogenase (l-lactate : NAD+ oxidoreductase, EC 1.1.1.27) isoenzymes purified from tissues of a poikilotherm (the snake Bothrops neuwiedii) and of a homeotherm (Ox). Inhibition of the ophidian isoenzyme B4 by high concentrations of pyruvate is suppressed at the upper limits of the temperature of the habitat. The data presented suggest that the temperature increment affects only the forces binding the pyruvate in the abortive ternary complex Enzyme-NAD+-pyruvate.

Effect of temperature upon catalytic properties of α-hydroxyacid dehydrogenase from Trypanosoma cruzi

A comparative study of the effect of temperature (10, 20, 30 and 37 degrees C) upon Km and V of alpha-hydroxyacid dehydrogenase (HADH), isozyme I and II, from Trypanosoma cruzi, a parasite whose life cycle comprises stages in an insect vector, and of another enzyme with analogous substrate specificity, the lactate dehydrogenase, isozyme X (LDH X) from mouse, a homeotherm, is presented. The Km for alpha-ketoisocaproate of HADH is markedly reduced as temperature decreases. This effect can compensate the reduction in thermal energy and produce stabilization of the reaction rate. This compensation does not occur with mouse LDH X. The activation energy for both HADH isozymes is about half the value determined for mouse LDH X. Results indicate that HADH from T. cruzi is able to adjust instantaneously to thermal changes of the environment, behaving as other enzymes of terrestrial poikilothermic animals.