The effect of normal red cell constituents on the activities of red cell enzymes

The effect of 2,3-DPG, pyridoxal-5′-P, pyridoxal, pyridoxine creatine and bicarbonate was studied on the activity of red cell glycolytic and pentose phosphate shunt enzymes at saturating and limiting substrate concentrations. 2,3-DPG strongly inhibits the activity of hexokinase, phosphoglucomutase, phosphofructokinase, aldolase and glyceraldehyde phosphate dehydrogenase. In the case of the first four enzymes, 2,3-DPG competes with the substrate and glyceraldehyde phosphate dehydrogenase is inhibited in a noncompetitive fashion. Pyridoxal-5′-P inhibits some of the enzymes inhibited by 2,3-DPG, including hexokinase, phosphoglucomutase, phosphofructokinase and aldolase; in addition, it also inhibits the activity of phosphoglucose isomerase, pyruvate kinase, glucose-6-P dehydrogenase and 6-phosphogluconate dehydrogenase. In some cases, the inhibition was competitive; in others, it was noncompetitive. Creatine and bicarbonate do not significantly inhibit any of the enzymes studied. The studies reported in this report indicate possible roles of 2,3-DPG and pyridoxal-5′-P in the regulation of glucose metabolism in red cells.