J. Biol. Chem., Vol. 256, Issue 20, 10306-10312, 10, 1981
Human hypoxanthine-guanine phosphoribosyltransferase. Purification and characterization of mutant forms of the enzyme
JM Wilson, BW Baugher, L Landa and WN Kelley
Erythrocyte hypoxanthine-guanine phosphoribosyltransferase has been highly
purified from five unrelated patients with a deficiency of this enzyme.
Affinity chromatography using either GMP-Sepharose or an immunoadsorbent
was the most productive step in the purifications. The specific activity of
the purified enzyme was unchanged for patients L. P. and G. S., and
slightly decreased for patient R. H., as compared to control subjects.
Enzyme from patient I. V. and from patient E. S. exhibited markedly reduced
specific activities when purified to near homogeneity. The level of
immunoreactive protein in patient I. V. appeared to be significantly higher
than normal. The apparent subunit molecular weight of the enzyme from
patient G. S. was decreased by approximately 1000 while it was increased by
approximately 400 from patient I. V. The isoelectric points of the subunit
isozymes were shifted to higher pH values from patients I. V. and E. S.,
and to lower pH values from patient L. P.; the subunit isozymes from
patient G. S. were identical with normal. These studies provide direct
evidence for the existence of at least four different mutations in the
structural gene for hypoxanthine-guanine phosphoribosyltransferase. The
four different mutant forms of human hypoxanthine-guanine
phosphoribosyltransferase that have been identified are named as follows:
patient L. P., HPRTToronto; patient G. S., HPRTLondon; patient E. S.,
HPRTKinston; and patient I. V., HPRTMunich.
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