Purification and characterization of rat kidney L-alanine: 4,5-dioxovalerate transaminase and inhibition by hemin

L-alanine: 4,5-dioxovalerate transaminase in Leishmania donovani that differs from mammalian enzyme

Leishmania protozoans are the causative agents of leishmaniasis, a major parasitic disease in humans. The parasites manifest a nutritional requirement for heme compounds since they are deficient in heme biosynthesis. In this study we have demonstrated for the first time the presence of the enzyme L-alanine: 4,5-dioxovalerate transaminase in Leishmania donovani. This enzyme catalyzes the synthesis of 5-aminolevulinic acid (ALA), the first committed step in heme synthesis. Thus the defect in heme biosynthesis pathway in Leishmania must lie at some enzymatic level subsequent to synthesis of ALA. The enzyme was found to be present in both virulent and avirulent strains of L. donovani. The virulent promastigotes showed a 41% higher specific activity as compared to the avirulent strain. The enzyme activity was found to be inhibited in the presence of heme and methylglyoxal. Immunoblot analysis revealed that L-alanine: 4,5-dioxovalerate transaminase in L. donovani was immunologically different from that in mammals.

Chicken eggshell porphyrins and the glyoxalase pathway: its possible physiological role

1. The plasma 4,5-dioxovaleric acid (DOVA) levels of two different breeds of chicken were determined and found to be higher in the group with a higher porphyrin eggshell content. 2. The erythrocyte and uterus glyoxalase II activity, investigated by means of a new spectrophotometric method, was found to be significantly higher in the group with a low porphyrin eggshell content. 3. A comparative genetic study of two chicken populations, one with white and one with dark eggshells, showed different gene frequencies for the glyoxalase I polymorphism. 4. An interpretation of these data suggests that the glyoxalase pathway may be involved in the metabolism of early porphyrin precursors.

Cytosolic L-alanine:4,5-dioxovalerate transaminase differs from the mitochondrial form

L-Alanine:4,5-dioxovalerate transaminase was detected in the kidney cytosolic fraction with a lower specific activity than the mitochondrial enzyme. The enzyme was purified from the cytosol to homogeneity with a yield of 32%, and comparative analysis with the mitochondrial form was performed. Both forms of the enzyme have identical pH and temperature optima and also share common antigenic determinants. However, differences in their molecular properties exist. The molecular mass of the native cytoplasmic enzyme is 260 kDa, whereas that of the mitochondrial enzyme is 210 kDa. In addition, the cytoplasmic L-alanine: 4,5-dioxovalerate transaminase had a homopolymeric subunit molecular mass of 67 kDa compared to a subunit molecular mass of 50 kDa for the mitochondrial L-alanine:4,5-dioxovalerate transaminase. This is the first report of two forms of L-alanine:4,5-dioxovalerate transaminase. The different responses of cytosolic and mitochondrial L-alanine:4,5-dioxovalerate transaminases to hemin supplementation both in vitro and in vivo was demonstrated. Maximum inhibition of mitochondrial L-alanine:4,5-dioxovalerate transaminase activity was demonstrated with hemin injected at a dose of 1.2 mg/kg body mass, whereas the same dose of hemin stimulated the cytosolic enzyme to 150% of the control. A one-dimensional peptide map of partially digested cytosolic and mitochondrial L-alanine:4,5-dioxovalerate transaminase shows that the two forms of the enzymes are structurally related. Partial digestion of the cytosolic form of the enzyme with papain generated a fragment of 50 kDa which was identical to that of the undigested mitochondrial form (50 kDa). Moreover, papain digestion resulted in a threefold increase in cytosolic enzyme activity over the native enzyme, and such enhancement was comparable to the activity of the mitochondrial form of the enzyme. Therefore, we conclude that the cytosolic form of L-alanine: 4,5-dioxovalerate transaminase is different from the mitochondrial enzyme. Furthermore, immunoblot analysis indicated that the mitochondrial enzyme has antigenic similarity to the cytosolic enzyme as well as to the papain-digested cytosolic enzyme 50-kDa fragment.

Production of delta-aminolevulinic acid: characterization of murine liver 4,5-dioxovaleric acid: L-alanine aminotransferase

1. We report on the kinetic properties of murine liver 4,5-dioxovaleric acid:L-alanine aminotransferase (DOVA transaminase). 2. The transamination of 4,5-dioxovaleric acid (DOVA) led to the production of delta-aminolevulinic acid. 3. L-Alanine was the preferred amino group donor among the common 20 amino acids. 4. The optimum pH of the reaction was 7-8. 5. A Km of 220 microM for DOVA and a Km of 970 microM for L-alanine were obtained. 6. The reaction was inhibited by each of the following: glyoxylate, beta-chloroalanine, methylglyoxal, delta-aminolevulinate, pyruvate, heme, and gabaculine. 7. None of several xenobiotic inducers of microsomal mixed function oxidases tested had a significant effect on DOVA transaminase activity in studies performed with murine primary hepatocyte cultures.

Characteristics of L-alanine:4,5-dioxovaleric acid transaminase: an alternate pathway of heme biosynthesis in yeast

The present study reports for the first time the presence of the enzyme L-alanine:4,5-dioxovaleric acid transaminase (EC 2.6.1.43), which catalyzes the irreversible synthesis of 5-aminolevulinic acid in three strains of yeast: Candida albicans 3100, Saccharomyces cerevisiae 3059, and S. cerevisiae S288C. The enzyme was predominantly present in the cytosol and was purified from C. albicans 3100 by about 200-fold with an overall yield of 23% to apparent homogeneity. The purification procedure involved heat treatment, followed by affinity chromatography on L-alanine-Sepharose CL-4B, ion-exchange chromatography on DEAE-cellulose DE-52, and chromatography on hydroxyapatite. As judged by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the enzyme appeared to be a monomeric protein of relative molecular mass 59,000. The enzyme activity was stimulated by pyridoxal phosphate and was optimally active at 60 degrees C. The purified enzyme had an isoelectric point of 4.7 and a pH optimum of 7.2 Km values of the enzyme for L-alanine, pyridoxal phosphate, and 4,5-dioxovaleric acid were 2.8 X 10(-7), 5.0 X 10(-7), and 1.05 X 10(-5) M, respectively. The Vmax of the enzymatic reaction was 5 X 10(-6) mol/mg/h. Antibody raised against the purified yeast L-alanine:4,5-dioxovaleric acid transaminase did not cross-react with the same enzyme from rat liver and kidney.

Production of delta-aminolevulinate: subcellular localization and purification of murine hepatic L-alanine: 4,5-dioxovaleric acid aminotransferase

1. L-Alanine: 4,5-dioxovaleric acid aminotransferase (DOVA transaminase) activity was measured in murine liver, kidney and spleen homogenates. 2. Among the organs examined, the specific activity of the enzyme was highest in kidney, followed by liver then spleen. 3. No differences in DOVA transaminase activity in kidney, liver and spleen homogenates were detected between mouse strains C57BL/6J and DBA/2J. 4. Based on enzyme activity, the capacity of DOVA transaminase to catalyze the formation of delta-aminolevulinic acid (ALA) in liver appeared much greater than the capacity of ALA synthase. 5. In DBA/2J animals, DOVA transaminase activity in liver mitochondrial fractions prepared by differential centrifugation was 24 nmol ALA formed/hr/mg protein compared with 0.63 nmol ALA formed/hr/mg protein for ALA synthase. 6. Cell fractionation analyses indicated that liver DOVA transaminase is located in the mitochondrial matrix. 7. The liver enzyme was purified from mitoplasts by chromatography on DEAE-Sephacel followed by affinity chromatography on L-alanine-AH-Sepharose. 8. The specific activity of the purified DOVA transaminase was 1600 nmol ALA formed/hr/mg protein. 9. The yield of the purification was ca 90 micrograms of protein per gram liver wet weight. 10. The purified enzyme had a subunit mol. wt of 146,000 +/- 5000 as determined by electrophoresis under denaturing conditions.

Affinity purification and properties of rat liver mitochondrial L-alanine:4,5-dioxovalerate transaminase and its inhibition by hemin

The present study describes a new rapid procedure for purification of L-alanine:4,5-dioxovalerate transaminase from rat liver mitochondria which was purified 243-fold with a 32% yield to apparent homogeneity. The purification procedure involved protamine sulfate treatment, followed by phenyl-Sepharose CL-4B column chromatography and alanine-Sepharose 4B affinity chromatography. The Km values for L-alanine and 4,5-dioxovalerate were 3.3 and 0.28 mM, respectively. The enzyme-bound pyridoxal phosphate content was estimated to be two molecules per enzyme molecule. The purified enzyme was inhibited by the reaction product pyruvic acid, substrate analog, methylglyoxal, and sulfhydryl inhibitors. Excess concentrations of 4,5-dioxovalerate was also found to inhibit the enzyme and our experiments failed to demonstrate reversibility of the reaction. Only hemin among the intermediate compounds of heme metabolism tested was shown to be an inhibitor of purified alanine:4,5-dioxovalerate transaminase. Hemin was further shown as an uncompetitive inhibitor of both alanine and dioxovalerate.

Evidence of hemin as an end product inhibitor of L-alanine: 4,5-dioxovalerate transaminase in rat liver mitochondria

This study describes the in vitro and in vivo effect of hemin on L-alanine:4,5-dioxovalerate transaminase activity. Hemin was shown to be an inhibitor of the purified enzyme and this inhibition was proportional to the concentration of hemin. The examined kinetic data with hemin showed uncompetitive inhibition for both alanine and 4,5-dioxovalerate. An apparent Ki of 30 and 42 microM for hemin were obtained with both alanine and 4,5-dioxovalerate, respectively. Moreover, the enzyme activity in liver was considerably decreased after the intravenous hemin administration and such an inhibition is dose and time dependent. Furthermore, maximum inhibition of the enzyme was observed 30 min after hemin injection and 60% enzyme inhibition was achieved with a dose of 1.2 mg/kg body wt of rat. Thus is suggests the important role of this enzyme on heme biosynthesis.