HUMAN LEUKOCYTE METABOLISM IN VITRO. I. INCORPORATION OF ADENINE-8-C14 AND FORMATE-C14 INTO THE NUCLEIC ACIDS OF LEUKEMIC LEUKOCYTES

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Abstract
Adenine was incorporated into RNA adenine and guanine by mature granulocytes, chronic lymphocytic leukemic (CLL), chronic myelocytic (CML) and acute leukemic (AL) leukocytes, and appears to reflect turnover rather than net synthesis of RNA. RNA purine incorporation of formate was enhanced by exogenous 5-amino-4-imidazole carboxamide (AIC) but was observed only in AL cells in the absence of exogenous AIC; de novo purine synthesis was inhibited by exogenous purines. Significant DNA purine incorporation was not observed. Formate incorporation into DNA thymine appears to reflect DNA synthesis; however, this could be enhanced by exogenous thymine precursors and inhibited by thymidine and its nucleotide in CML cells, but not in CLL or AL cells. Thus, leukemic cell nucleic acid base synthesis is variably affected by exogenous precursors or products. The incorporation pattern of CML cells suggests that their RNA nucleotides are utilized for DNA synthesis. The low rate of apparent DNA synthesis observed in some AL leukocytes may reflect a block in this postulated conversion of RNA to DNA.