The rate of 3-phosphoglycerate kinase reaction carried out under the conditions of saturating substrate concentrations (10 mM 3-phosphoglycerate, 3 mM ATP) and 0.2 mM NADH is increased in the presence of glyceraldehyde-3-phosphate dehydrogenase. This effect is probably due to the acceleration of 1.3-diphosphoglycerate transfer in the bienzyme complex (Weber and Bernhard, Biochemistry, 21,4189-4194, 1982). An analysis of the dependence of the rate constant of the coupled 3-phosphoglycerate kinase- glyceraldehyde-3-phosphate dehydrogenase reaction on the concentration of the latter enzyme was used to estimate the apparent Kd of the bienzyme complex. Under the conditions employed in this study (MOPS, 20 mM pH 7.2, 25 degrees C) this value was found to correspond to (2.5 +/- 0.6). 10(-8)M.