THE KINETICS AND MECHANISM OF A REACTION CATALYZED BY BACILLUS-STEAROTHERMOPHILUS PHOSPHOGLUCOSE ISOMERASE

The initial rates of isomerization between glucose 6-phosphate and fru ctose 6-phosphate catalyzed by Bacillus stearothermophilus phosphogluc ose isomerase (PGI) were measured in both the forward and reverse reac tions. Although B. stearothermophilus PGI is a tetrameric enzyme, the reaction rate vs substrate concentration curves for both reactions exh ibited Michaelis-Menten kinetic behavior. This was confirmed by the Hi ll plot which gave the Hill coefficient of 1.0 for both reactions. Bas ed on the above experimental results and another experimental result t hat the number of substrate or product binding sites on the PGI molecu le was 4, we propose a reaction scheme which is able to explain Michae lis-Menten kinetic behavior of this oligomeric enzyme, and determine t he kinetic parameters.