PT  - JOURNAL ARTICLE
AU  - DAVID KESSEL
AU  - JUDITH DEACON
AU  - BARBARA COFFEY
AU  - ANN BAKAMJIAN
TI  - Some Properties of a Pyrimidine Phosphoribosyltransferase from Murine Leukemia Cells
DP  - 1972 Nov 01
TA  - Molecular Pharmacology
PG  - 731--739
VI  - 8
IP  - 6
4099  - http://molpharm.aspetjournals.org/content/8/6/731.short
4100  - http://molpharm.aspetjournals.org/content/8/6/731.full
SO  - Mol Pharmacol1972 Nov 01; 8
AB  - A pyrimidine phosphoribosyltransferase (approximate mol wt 100,000) with a sharply defined specificity was partially purified from ascitic cells of the P388/38280 murine leukemia. This enzyme is involved in the conversion of the antineoplastic drug 5-fluorouracil (Km = 100 µM) to pharmacologically active nucleotides. The lowest Km value was obtained with orotic acid as substrate (Km 50 µM). The enzyme could also utilize 5-fluoroorotate (Km 85 µM) and uracil (Km = 5 mM). Inhibition studies, using fluorouracil as substrate, indicate that this enzyme has a strong affinity for pyrimidines with a carboxyl or amino group at position 6, or a fluorine (but not a larger halogen) at position 5. A methyl group at position 5 markedly decreases affinity of the enzyme for all pyrimidines. The affinity of the enzyme for 6-carboxypyrimidines was greatly increased in the presence of dimethylsulfoxide, but the rate of the enzyme-catalyzed reaction was markedly decreased. The enzyme requires Mg2+ and phosphoribosyl pyrophosphate; the latter promotes stability at all temperatures. Enzyme extracted from a cell line made resistant to fluorouracil showed a decreased capacity to utilize fluorouracil as a substrate.