Purine nucleoside phosphorylase of the malarial parasite, Plasmodium lophurae.
Purine nucleoside phosphorylase (EC 2.4.2.1, purine nucleoside:orthophosphate ribosyltransferase) was purified and characterized from the malarial parasite, Plasmodium lophurae, using a chromatofocusing (Pharmacia) column and a formycin B affinity column. The apparent isoelectric point of the native protein, as determined by chromatofocusing, was 6.80. By gel filtration and both native and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the native enzyme appeared to be a pentamer with a native molecular weight of 125,300 and a subunit molecular weight of 23,900. The enzyme had a broad pH optimum, pH 5.5-7.5, with maximum activity at pH 6.0-6.5. The enzyme reaction was readily reversible with a Km for inosine of 33 microM and a Km for hypoxanthine of 82 microM. Thioinosine, guanosine, and guanine were also substrates for the plasmodial enzyme, but allopurinol and adenine were not. The parasite enzyme was competitively inhibited by formycin B (Ki = 0.39 microM). Formycin A, azaguanine, and 8-aminoguanosine were not inhibitors of the enzyme.
D000818:Animals; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D005573:Formycins / Q000494:pharmacology; D007525:Isoelectric Focusing; D007700:Kinetics; D008970:Molecular Weight; D010430:Pentosyltransferases / Q000378:metabolism*; D010961:Plasmodium / Q000201:enzymology*; D011683:Purine-Nucleoside Phosphorylase / Q000378:metabolism*
D005573:Formycins; C034561:formycin B; C034550:formycin; D010430:Pentosyltransferases; D011683:Purine-Nucleoside Phosphorylase