Human adenine phosphoribosyltransferase: characterization from subjects with a deficiency of enzyme activity.

Adenine phosphoribosyltransferase (APRT) was characterized with respect to specific activity and immunoreactive protein (CRM) levels in hemolysate from 18 members of an APRT-deficient kindred. In addition, lymphoblastoid cell lines were established from six of these subjects and APRT from these cells was characterized in a similar fashion. Levels of specific activity and CRM in patients homozygous for the deficiency were less than 1% of normal. Heterozygous subjects had higher levels of activity and CRM in lymphoblasts than in erythrocytes and, in all cases, the APRT present was normal in terms of isoelectric point, subunit molecular weight, and heart stability. The higher levels of activity and CRM found in lymphoblasts may be due either to expression of a mutant gene product stabilized in a normal:mutant dimer or to autologous regulation.