THE METABOLISM OF THE ERYTHROCYTE: XVII. MECHANISM OF INCORPORATION OF ADENINE INTO AND RESULTANT ELEVATION OF ATP AND ADP IN HUMAN ERYTHROCYTES

Abstract

Human erythrocytes were incubated for 48 hours at 37 °C with adenine-8-14C and glucose. The incorporation of the adenine into nucleotides continued for 10–14 hours, most of the radioactivity being found in the ATP. Degradation of the nucleotides then commenced. In the absence of glucose, the breakdown of the newly synthesized ATP followed the pathway ATP → ADP → AMP → inosine → hypoxanthine. The breakdown of adenine-labeled ATP could be delayed beyond 10–14 hours if the incubation medium containing glucose was changed periodically. The specific activities of the adenine nucleotides during incorporation of adenine-8-14C were in the order AMP > ADP > ATP. Molar incorporation of pentose carbons from glucose-U-14C approached that of the adenine-8-14C, provided the pool of glycolytic intermediates had been labeled by preincubation with glucose-U-14C. The increase in the level of nucleotide-labile phosphate found experimentally corresponded to that calculated on the basis of adenine-8-14C incorporation into ATP and ADP. The level in labile phosphate was twice that found in fresh cells. It is concluded that adenine is incorporated via the pathway adenine → AMP → ADP → ATP, and that this may serve as a mechanism for raising the level of ATP in the erythrocyte at least twofold.