Transfer of 1,3-diphosphoglycerate between glyceraldehyde 3-phosphate dehydrogenase and 3-phosphoglycerate kinase via an enzyme-substrate-enzyme complex

Abstract

On the basis of the alternatives of direct interenzyme transfer vs. dissociation followed by random diffusion, 2 kinetic models for metabolite transfer between consecutive enzymes are developed. These 2 models are readily distinguishable experimentally for the transfer of 1,3-diphosphoglycerate (1,3-P2G) between [halibut, rabbit muscle] glyceraldehyde-3-phosphate dehydrogenase (GPDH) and 3-phosphoglycerate kinase (PGK). Since 1,3-P2G is exceedingly tightly bound to PGK, the kinetics of its transfer to GPDH are predictably different for each of these 2 models. 1,3-P2G is directly transferred between these 2 enzymes via an enzyme-substrate-enzyme complex. This direct transfer is described by a Michaelis-Menten scheme in which PGK.cntdot.1,3-P2G is the substrate for GPDH. At high concentrations of PGK.cntdot.1,3-P2G, the transfer reaction becomes nearly PGK.cntdot.1,3-P2G concentration independent. The rate of the transfer reaction is activated 3.5-fold by saturating quantities of ATP and 20-fold by saturating quantities of 3-PG. Evidence is presented that the PGK.cntdot.1,3-P2G complex is structurally distinct from either PGK itself or other PGK.cntdot.ligand complexes.