Purine metabolism of human erythrocytes during storage and physiological conditions.
Some results from storage experiments at +4 degrees C with adenine and purine nucleosides (cf. [1]) are compared with incubation experiments at 37 degrees C with guanosine at pH 7.0 and 7.4 and three different levels of inorganic phosphate (iP). At the lower pH and 20 mmol . l-1 iP the synthesis of GTP was extremely rapid; the intracellular concentration reached 0.5 mmol . l-1 within 25 min constituting 1/3 of the purine nucleoside triphosphate pool. Replacement of ATP by an ATP-GTP mixture has metabolic effects on several enzymic steps, e.g., phosphofructose kinase and phosphoglycerate kinase explaining the reported beneficial effect on human erythrocytes during preservation. In order to explore the role of erythrocytes in the physiological transport of purines and purine nucleosides in vitro experiments were designed in which the substances were continuously added to the appropriate concentrations by means of a dialysis tubing. Prior to incubation the erythrocytes were stored with NaF in order to reduce the total adenylate concentration. The rate of synthesis of adenylates was about 0.05 mmol . h-1 (calculated per litre of erythrocytes) both when adenosine and adenine were supplied as source for the adenine moiety of the adenylates. Analyses of purines, nucleosides, glucose, lactate and iP in the efferent dialysis solution and the extra- and intracellular volumes reveal the metabolic processes in the erythrocytes if the transport across the dialysis tubing is accounted for. The low capacity of the erythrocyte adenylate synthesis indicates that only a minor part of the adenine compounds physiologically exported by the liver could be delivered as intraerythrocytic adenylates.