Kinetic pathways of formation and dissociation of the glycerol-3-phosphate dehydrogenase-fructose-1,6-bisphosphate aldolase complex.

Quantitative analysis of the time courses of fluorescence anisotropy changes due to the binding of fructose-1,6-bisphosphate aldolase to the dissociable cytoplasmic glycerol-3-phosphate dehydrogenase covalently labelled with fluorescent dye was carried out. The behaviour of the aldolase-dehydrogenase system seems to be consistent with a cyclic reversible model characterized by the formation and dissociation of complexes of both the monomeric and the dimeric forms of dehydrogenase with aldolase, and rapid equilibrium between the free monomeric and dimeric forms of dehydrogenase. The half-life time of the formation of dimeric dehydrogenase-aldolase complex at the concentration of the enzymes expected to exist in the cell (i.e. in the micromolar range) is some minutes, and the time needed for equilibration between the aldolase-bound dimeric and monomeric forms of dehydrogenase is a few minutes as well. Consequently, one may expect that both the formation and the dissociation of this heterologous enzyme complex have physiological relevance.