Studies of the metabolism of human erythrocyte membranes.

These investigations were undertaken to discover whether the membrane of the mature human erythrocyte is capable of metabolic activity that could possibly provide the means for active transport. Hoffman (2) has clearly shown that ATP provides energy for sodium transport, and it has been assumed that ATP for this process is supplied from within the erythrocyte. It seemed reasonable to examine membranes not only for possible sources of ATP production, but also for segments of metabolic pathways that could function as specific transport systems. Two methods have been in general use for the study of the enzymic composition of membranes (3). In one, whole cells are incubated with substrates or inhibitors to which the membrane is known to be impermeable. Any change in the external medium is then taken to represent enzymic activity present on the outer surface of the membrane. In the second method., labeled, permeable substrates are added to the medium, and after relatively short intervals, labeled compounds are extracted from the interior of cells and identified. The enzymic activity of the membrane is then deduced from the observed changes in substrates. Both methods have been useful, but neither can provide information about the organization of enzymes in the membranes. For this purpose, it is necessary to prepare and study erythrocyte membranes themselves. In the present study, morphologically intact homogeneous membranes, virtually free of hemoglobin, were prepared by dialysis of human erythrocytes against increasingly hypotonic saline