Leukocyte purine phosphoribosyltransferases in human leukemias sensitive and resistant to 6-thiopurines.

The levels of leukocyte adenine phosphoribosyltransferase and of hypoxanthine-guanine phosphoribosyltransferase (H-GPRT) were compared in normal control subjects, patients with acute leukemia in remission, and patients with acute leukemia in exacerbation. Significant (p < 0.025) elevations of both the adenine phosphoribsosyltransferase and H-GPRT activities occurred in individuals with leukemia in relapse, compared with those in remission. Altered ratios of the specific enzymatic activities of adenine phosphoribosyltrans ferase to H-GPRT were noted in two of eight 6-thiopurineresistant patients. Leukemic cells from one patient with chronic myelogenous leukemia in blast crisis exhibited a marked decrease in H-GPRT activity. The H-GPRT from the second patient showed an altered affinity for purine bases and, most markedly, for 5'-phosphoribosyl-1-pyrophosphate when