The Role of Direct Phosphorylation in the Mechanism of Adenosine Utilization for Nucleotide Synthesis in Mouse Erythrocytes*

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Abstract
The contribution of adenosine as a source of red cell nucleotides and the significance of direct phosphorylation of this nucleoside in nucleotide formation were investigated in peripheral mouse erythrocytes. 1. Radiochemical methods for the analysis of nucleotides in mouse erythrocytes were used following treatment of the cells with adenosine-u-14C. The relative significance of various metabolic pathways of adenosine in relation to nucleotide synthesis was evaluated quantitatively from the results obtained. 2. Mouse erythrocytes were incubated with adenosine-u-14C in vitro. Cells incorporated whole adenosine molecules into their nucleotide pool by direct phosphorylationand to some extent also incorporated the base moiety formed by cleavage of the nucleoside following deamination. The lower the concentration of adenosine, the more predominant was the former pathway. 3. Various amounts of adenosine-u-14C were injected intravenously into mice to get plasma concentrations of nucleoside in the range from 10−8 to 10−4M. The in vivo mode of adenosine incorporation into red cell nucleotides was found to be direct phosphorylation under the conditions employed. 4. Elimination of inosine-8-14C radioactivity from the animals after intravenous administration was faster than that of adenosine-8-14C. In intact mice, radioactivity in tissues after administration of adenosine-8-14C was higher than that after inosine-814C. 5. The results were discussed in relation to the physiological role of adenosine incorporation into the nucleotides of circulating erythrocytes.

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