Yp. Dai et al., PROPERTIES OF URACIL PHOSPHORIBOSYLTRANSFERASE FROM GIARDIA-INTESTINALIS, International journal for parasitology, 25(2), 1995, pp. 207-214
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.