PROPERTIES OF URACIL PHOSPHORIBOSYLTRANSFERASE FROM GIARDIA-INTESTINALIS

Dal Y.-P., Lee C. S. and O'Sullivan W. J. 1995. Properties of uracil p hosphoribosyltransferase from Giardia intestinalis. International Jour nal for Parasitology 25: 207-214. Incorporation of pyrimidine ribonucl eotides in Giardia intestinalis occurs via uracil phosphoribosyltransf erase (UPRTase). The enzyme was purified over 1000-fold to apparent ho mogeneity from parasite extracts, using Fast Protein Liquid Chromatogr aphy, namely Mono Q anion exchange, Mono P chromatofocusing and Supero se 12 chromatography. The specific activity of the purified enzyme was 3100 nmol min(-1) mg protein(-1). The enzyme was found to be a dimer of mel. wt. 76,000. Kinetic analysis, including initial velocity and p roduct inhibition studies, indicated that it obeyed a rapid-random equ ilibrium mechanism. GTP and dGTP caused a dramatic increase in the act ivity of the enzyme, though there was no effect on the Michaelis const ants. All other nucleotides tested were without effect or were inhibit ory. The effect of GTP is similar to that observed for UPRTase from E. coli but not from other eukaryotes.