Specificity in the Association of Glyceraldehyde 3-Phosphate Dehydrogenase with Isolated Human Erythrocyte Membranes

Abstract

Abstract We have characterized the binding of glyceraldehyde 3phosphate dehydrogenase to isolated human erythrocyte membranes in an effort to establish whether this in vitro association has physiologic significance. At pH 8 and µ = 0.015 m, approximately 2 x 106 glyceraldehyde-3-P dehydrogenase molecules bound reversibly and homogeneously to the inner (but not the outer) membrane surface with an association constant of 1 x 107 m-1. This binding capacity exceeded by roughly 10-fold the cell's glyceraldehyde-3-P dehydrogenase content. Binding diminished with increasing ionic strength and pH, suggesting a strong electrostatic component in the association. Millimolar amounts of certain metabolites also released bound enzyme from the membrane. In contrast, an indifferent strongly basic protein, cytochrome c, lacked specificity in its association with the erythrocyte membrane. That is, binding was relatively weak, occurred at both membrane surfaces, and may have been limited in extent by close packing (i.e. monolayer formation) rather than by a fixed number of binding sites. Cytochrome c showed much stronger association with carboxymethylcellulose than did glyceraldehyde-3-P dehydrogenase, but was more readily eluted from the membrane by electrolytes. Cytochrome c binding to membranes was not altered by any metabolite tested. We hypothesize that a fraction of erythrocyte glyceraldehyde-3-P dehydrogenase may be specifically bound to the inner surface of the membrane in vivo in a fashion which is responsive to metabolic and ionic transients.