Heme synthesizing enzymes of Plasmodium knowlesi: a simian malaria parasite.

Intraerythrocytic stages of cell-free Plasmodium knowlesi possess significant activities of heme biosynthetic enzymes, viz. delta-aminolevulinic acid synthase (delta-ALAS), delta-aminolevulinic acid dehydrase (delta-ALAD), ferrochelatase (FC), and tryptophan pyrrolase (enzyme representing free heme pool). delta-Aminolevulinic acid synthase and FC showed higher activities in schizont than in ring trophozoite stage. Uninfected monkey erythrocytes did not possess the above-mentioned enzyme activities; on the contrary, leucocytes showed detectable enzyme activities. delta-Aminolevulinic acid synthase was not appreciably inhibited by different antimalarials. Succinyl acetone and hemin exhibited a concentration-dependent inhibition of delta-ALAD and delta-ALAS, respectively.