Binding Studies on Rabbit‐Muscle Phosphoglucose Isomerase

Binding studies utilizing the techniques of gel filtration, rate dialysis and equilibrium dialysis yielded a value of 2.0 binding sites per molecule for either substrate or inhibitors like 6‐phospho‐gluconate and pyridoxal 5′‐phosphate to rabbit muscle phosphoglucose isomerase, thereby establishing that the enzyme has one catalytic site per subunit. For the substrates and 6‐phospho‐gluconate studies were performed at various pH values. For 6‐phosphogluconate, the dissociation constant was found to change dramatically with increasing pH, following a pattern analogous to that deduced from catalytic rate measurements. For the catalytic equilibrium mixture of glucose 6‐phosphate and fructose 6‐phosphate, the Kd showed excellent agreement with the Km values reported earlier. The binding studies are discussed in relation to the current concept of the catalytic mechanism.