Hypoxanthine phosphoribosyltransferase deficiency: association of reduced catalytic activity with reduced levels of immunologically detectable enzyme protein.

In the present study hemolysates from fourteen patients with a genetically determined deficiency of hypoxanthine phosphoribosyltransferase (EC 2.4.2.8; IMP:pyrophosphate phosphoribosyltransferase) activity were examined immunologically for the presence of material that crossreacts with the normal enzyme. A quantitative assay for crossreacting material in enzyme-deficient hemolysates was based on the inhibition of the immunoprecipitation of the normal enzyme. As little as 3% of normal crossreacting material could be detected. One patient in this series was found to have a normal amount of crossreacting material, whereas the remainder had no detectable crossreacting protein. The lack of detectable crossreacting material in these patients raises the possibility that a defect in synthesis or degradation of enzyme protein may be present in many patients deficient in hypoxanthine phosphoribosyltransferase.