Glyceraldehyde-3-phosphate dehydrogenase release from erythrocytes during haemolysis. No evidence for substantial binding of the enzyme to the membrane in the intact cell

Glyceraldehyde-3-phosphate dehydrogenase (G3PDH, EC 1.2.1.12) release from haemolysing erythrocytes, and its redistribution between free and membrane-bound states, were studied with a new type of rapid-mixing filtration apparatus. The apparatus is described. The results indicate that the rate of G3PDH appearance in filtrates is determined not only by the enzyme redistribution but also by the kinetics of haemolysis. We have quantified the extent of haemolysis as a function of time, by measuring the amounts of filterable K+ and lactate dehydrogenase. These are cytoplasmic components that are not membrane-bound. When we correct for incomplete haemolysis, extrapolation to zero times indicates that very little G3PDH is membrane-bound in the intact cell.