Induction of L-alanine:4,5-dioxovalerate transaminase by phenylhydrazine is associated with depletion of heme level

Markers for vulnerability in acute porphyria. A hypothesis paper

Previously symptomatic and permanently asymptomatic carriers of a gene mutation for acute intermittent porphyria as well as matched controls were screened with regard to a series of variables of possible relevance to the development of porphyric symptoms. The basis for the study was a concept of acute porphyria as a condition of a permanent system overload of oxidative stress, with long term effects on hepatic and renal tissue, and with instances of periodic overload of free radicals giving rise to acute neurologic involvement. Leukocyte concentrations of manganese, calcium, iron and zinc, as well as erythrocyte calcium differed between the groups, acute intermittent porphyria gene carriers, irrespective of previous porphyric illness, showing significantly higher levels than the controls. Manganese was found to be the most discriminative component of all the 78 variables investigated, accounting for about 98 per cent of the variance between the groups. An increment, by a factor of four, in cellular manganese is suggestive of an increase, in acute intermittent porphyria, of a manganese associated enzyme, e.g. glutamine synthetase, pyruvate carboxylase or mitochondrial superoxide dismutase. The best fit into the model considered is provided by a theory focused on superoxide dismutase, induced in response to superoxide anion radical produced from aminolaevulinic acid. In porphyria gene carriers seemingly resistant to porphyric manifestations, an increase in potentially prooxidant cellular iron is matched by a proportional increment in manganese, i.e. presumably by a corresponding mitochondrial superoxide dismutase induction. This mechanism is not operative in porphyric individuals prone to development of neuropsychiatric symptoms. In acute intermittent porphyria with a history of porphyric illness there is a positive correlation between erythrocyte manganese and serum folate and a negative correlation between leukocyte ferrochelatase activity and serum cobalamin concentration. This may mirror a role of the cobalamin-folate system in the acute porphyric process.

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.

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.

Nonenzymatic synthesis of delta-aminolevulinate (ALA) by cobalt (Co++)

Cobalt, a metal known to modulate the heme biosynthetic enzymes, is shown to be capable of catalysing the formation of ALA through a transamination reaction. The transamination reaction follows a double-displacement reaction kinetics. Further, it has also been shown that the product of the reaction catalysed by cobalt can be used by the enzyme ALA dehydratase as the substrate in the formation of porphobilinogen. The formation of ALA by cobalt can be inhibited by the intermediates of the heme biosynthetic pathway, mainly protoporphyrin. Heme, on the other hand, does not have any effect on the reaction at all concentrations tested.