Activities of phosphoribosyltransferase for
hypoxanthine and
adenine were investigated in erythrocytes and human tissues of fetuses and adults as well as in cultivated fibroblasts and amniotic fluid cells. Kinetic characteristics of these
enzymes were also studied in patients with the
Lesch-Nyhan syndrome and with partial deficiency for
hypoxanthine phosphoribosyltransferase (HGPRTase), and their obligate heterozygotes. The affinity of HGPRTase for both substrates in partial deficiency decreased to 13 to 20% of normal and by a less degree in its heterozygotes (50 to 65% of normal). A slight decrease in the Km for phosphoribosylpyrophosphate was observed in the case of heterozygotes for the
Lesch-Nyhan syndrome. Elevated erythrocytic
adenine phosphoribosyltransferase (
APRTase) activity was found in fetuses, patients with the
Lesch-Nyhan syndrome or with partial deficiency, and in some heterozygotes as well. However, the Km of
APRTase for
hypoxanthine in these subjects was the same as that in the normal adults. The HGPRTase activity in liver increased almost 4 times during the developmental period, whereas the
APRTase activity remained approximately the same. In fetal liver, the
APRTase activity was almost two times higher than the HGPRTase activity, whereas in fetal brain the HGPRTase activity was higher. The Km of HGPRTase for
hypoxanthine in cultivated cells and human tissues were similar to that in erythrocytes and leukocytes. On the other hand, the HGPRTase affinity for phosphoribosylpyrophosphate in these cells was cconsiderably larger than in erythrocytes or in leukocytes.