Alternative Pathways of Deoxyadenosine and Adenosine Metabolism

The relative rates of phosphorylation, deamination, and cleavage of deoxyadenosine and adenosine were examined in Ehrlich ascites tumor cells; mouse, human, and sheep erythrocytes; and mouse brain, heart, kidney, and liver. Cleavage of deoxyadenosine was measured by the formation of adenine ribonucleotides and phosphorylation by the formation of adenine deoxyribonucleotides; deamination of deoxyadenosine was inhibited by coformycin. All of the tissues examined exhibited a low but measurable ability to cleave the glycosidic bond of deoxyadenosine. The deoxyadenosine kinase to cleavage ratio was greatest, 3.5 to 6, in erythrocytes, 2.1 for Ehrlich ascites tumor cells, and near unity for mouse tissues. In the absence of the adenosine deaminase inhibitor, deamination was the major route of deoxyadenosine metabolism in mouse brain, heart, kidney, and liver and in mouse and human erythrocytes, whereas phosphorylation and deamination were nearly equivalent in sheep erythrocytes. At low substrate concentrations (less than 150 µ m ) more adenosine was phosphorylated than deaminated in Ehrlich ascites tumor cells.