Human hypoxanthine phosphoribosyltransferase. Purification and properties

Abstract
Hypoxanthine phosphoribosyltransferase (IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) from human erythrocytes was purified 13,000-fold to apparent homogeneity. The native enzyme has a sedimentation coefficient of 5.9 S, determined by analytical ultracentrifugation, and a MW of 81,000-83,000, determined by sedimentation equilibrium centrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates a subunit MW of 26,000, suggesting that the enzyme is a trimer. Isoelectric focusing resolves 3 peaks of enzyme activity at pH 5.6, 5.7 and 5.9. The amino acid composition of hypoxanthine phosphoribosyltransferase is 17 Lys, 5 His, 12 Arg, 0 Trp, 31 Asx, 12 Thr, 14 Ser, 16 Glx, 14 Pro, 19 Gly, 12 Ala, 5 Cys, 18 Val, 5 Met, 11 Ile, 20 Leu, 10 Tyr and 9 Phe. The enzyme appears to have a blocked N terminus.