L-ALANINE-4,5-DIOXOVALERATE TRANSAMINASE IN LEISHMANIA-DONOVANI THAT DIFFERS FROM MAMMALIAN ENZYME

Leishmania protozoans are the causative agents of leishmaniasis, a maj or parasitic disease in humans. The parasites manifest a nutritional r equirement for heme compounds since they are deficient in heme biosynt hesis. In this study we have demonstrated for the first time the prese nce of the enzyme L-alanine: 4,5-dioxovalerate transaminase in Leishma nia donovani. This enzyme catalyzes the synthesis of 5-aminolevulinic acid (ALA), the first committed step in heme synthesis. Thus the defec t in heme biosynthesis pathway in Leishmania must lie at some enzymati c level subsequent to synthesis of ALA. The enzyme was found to be pre sent in both virulent and avirulent strains of L. donovani. The virule nt 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 immu nologically different from that in mammals.