31P NMR studies of enzyme-bound substrate complexes of yeast 3-phosphoglycerate kinase. 2. Structure measurements using paramagnetic relaxation effects of Mn(II) and Co(II).

Measurements of the paramagnetic effects of two dissimilar activating paramagnetic cations, Mn(II) and Co(II), on the spin relaxation rates of the 31P nuclei in the complexes of 3-phosphoglycerate kinase with ATP, ADP, and 3-P-glycerate have been used to study the structures of these enzyme-substrate complexes. All experiments were performed on enzyme-bound complexes, so that two exchanging complexes (with and without cation) contribute to the observed relaxation rate. Measurements were made at three 31P NMR frequencies, 81, 121.5, and 190.2 MHz, and as a function of temperature in the range 5-20 degrees C to determine the effect of exchange on the observed relaxation rates. Relaxation rates in E.MnADP and E.MnATP were shown to be exchange-limited, and therefore bereft of structural information, both by lack of frequency dependence and by temperature dependence with activation energies (delta E) in the range 5-8 kcal/mol. Relaxation rates for E.CoADP and E.CoATP exhibit frequency dependence and delta E values in the range 1-3 kcal/mol; i.e., these rates depend on the Co(II)-31P distances. Difficulties involved in estimating electron relaxation times in E.CoADP and E.CoATP restrict calculation of Co(II)-31P distances in these complexes to upper and lower limits. These distances were all in the range 2.7-4.1 A, appropriate for direct coordination of Co(II) to the phosphate groups.(ABSTRACT TRUNCATED AT 250 WORDS)