Hexokinase, aldolase, glyceraldehyde-3-phosphate dehydrogenase, pyruvate kinase and glutamic-oxalacetic transaminase activities, and the rate of glycolysis have been measured in red cells from seven adult males responding to repeated phlebotomy or erythropheresis with iron replacement. The change in median age of the red cell populations of these men was estimated from the measured rates of red cell loss and erythropoietic replacement. These enzyme activities and glycolytic rates were measured also in a patient with aplastic anaemia in whom transfused red cells were aging at a known rate.
Hexokinase, aldolase and transaminase activities in the youngest red cell populations were four times greater than the corresponding levels in normal aged cell populations. Pyruvate kinase activity was two or three times higher than normal, but glyceraldehyde-3-phosphate dehydrogenase activity was not significantly increased in the youngest cell populations. The rate of glycolysis in intact cells and of lactate formation from glucose or glucose-6-phosphate in coenzyme-supplemented haemolysate showed a two-fold increase above normal in the youngest cell populations. Subnormal enzyme activity in older cells was observed only for transaminase.
The deterioration of hexokinase and aldolase activity with red cell aging is sufficiently rapid and the activity of these enzymes is normally sufficiently low to indicate a severe glycolytic limitation in old red cells. Such limitation in glycolysis may impair red cell viability and be the determining factor in normal red cell life span.
Measurement of activity of hexokinase, aldolase, or glutamic-oxalacetic transaminase in an unknown red cell population should indicate the median age of the cell population much sooner than such information can be obtained by measurement of red cell survival.