title: Characterization of adenine phosphoribosyltransferase from the human malaria parasite, Plasmodium falciparum.
abstract: Because of their inability to synthesize purines de novo, malaria parasites rely on purine phosphoribosyltransferases (PRTases) to convert purine bases salvaged from the host cell (the erythrocyte) into the corresponding purine nucleoside monophosphates. Our studies with late trophozoites of the human malaria parasite, Plasmodium falciparum, showed that virtually all of the purine PRTase activity is accounted for by two distinct enzymes. One enzyme utilizes hypoxanthine, guanine and xanthine (Queen, S.A., Vander Jagt, D. and Reyes, P. (1988) Mol. Biochem. Parasitol. 30, 123-134). The second enzyme utilizes only adenine and is the subject of this paper. This latter enzyme exhibits a biphasic pH-activity profile and is moderately to weakly inhibited by several divalent metal ions. Several of the properties of the P. falciparum enzyme were found to differ significantly from those of human erythrocyte adenine PRTase. (1) The molecular weight (18,000) of the parasite enzyme is smaller than that of the host cell enzyme. (2) The parasite enzyme, unlike the erythrocyte enzyme, is not significantly inhibited by sulfhydryl reagents. (3) 6-Mercaptopurine and 2,6-diaminopurine proved to be competitive inhibitors of the parasite enzyme (Ki 0.70 and 1.0 mM, respectively); on the other hand, the human enzyme is not inhibited by these agents. (4) The Km for adenine (0.80 microM) and 5-phosphoribosyl-1-pyrophosphate (0.70 microM) displayed by the parasite enzyme are significantly smaller than the corresponding Km values shown by the erythrocyte enzyme. These distinctions between the parasite and host enzymes point to the possibility that adenine PRTase of P. falciparum may represent a potential target for chemotherapeutic attack.
authors.affiliation: Department of Biochemistry, University of New Mexico School of Medicine, Albuquerque 87131.
authors.forename: S A
authors.initials: SA
authors.lastname: Queen
authors.forename: D L
authors.initials: DL
authors.lastname: Vander Jagt
authors.forename: P
authors.initials: P
authors.lastname: Reyes
mesh_terms: D000228:Adenine Phosphoribosyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D002413:Cations, Divalent / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D004912:Erythrocytes / Q000201:enzymology; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D010430:Pentosyltransferases / Q000378:metabolism*; D010963:Plasmodium falciparum / Q000201:enzymology*; D011687:Purines / Q000378:metabolism / Q000494:pharmacology; D013439:Sulfhydryl Reagents / Q000494:pharmacology
chemical_list: D002413:Cations, Divalent; D011687:Purines; D013439:Sulfhydryl Reagents; D010430:Pentosyltransferases; D000228:Adenine Phosphoribosyltransferase