METABOLISM OF ADENOSINE AND DEOXYADENOSINE BY HUMAN ERYTHROCYTES AND CCRF-CEM LEUKEMIA-CELLS

Human lymphocytes lacking adenosine deaminase die and T-cell leukemias are killed by deoxycoformycin (dCf), an inhibitor of adenosine deamin ase, due to impaired metabolism of dAdo. The initial metabolism of exo genous adenosine (Ado) and deoxyadenosine (dAdo) has been compared in human erythrocytes and CCRF-CEM leukemia cells and the data obtained h ave been simulated using kinetic constants obtained in vitro for the e nzymes involved. Cells were mixed with H-3-labelled Ado or dAdo, sampl es were taken at 3 sec intervals and progress curves for the H-3-label led metabolites formed were determined by quantitative two-dimensional thin layer chromatography. Erythrocytes rapidly take up Ado and the p redominant metabolite after 60 sec is hypoxanthine (Hyp), while for dA do, deoxyinosine (dIno) predominates. By contrast, leukemia cells conv ert Ado predominantly to AMP, while dAdo is converted first to Hyp and then to AMP. The presence of dCf had little effect upon Ado metabolis m but induced accumulation of dAdo. Erythrocytes rapidly degrade Ado a nd dAdo to Hyp, although the phosphorolysis of dIno is relatively slow . Human CCRF-CEM leukemia cells convert most of the Ado or dAdo to AMP after 60 sec. For dAdo, the sequence of reactions would be dAdo-->dIn o-->Hyp-->IMP-->sAMP-->AMP. dCf does not significantly affect the conv ersion of Ado-->AMP, but dCf blocks AMP accumulation from dAdo, consis tent with the reaction sequence shown above. A computer model has been developed for the metabolism of Ado and dAdo, but some of the kinetic constants determined in vitro for this model do not pertain to intact cells. Copyright (C) 1996 Elsevier Science Ltd