Studies on the mechanisms of the aldose-ketose isomerases will include: the Km and Vmax of 5 deoxy fructose-6-P with phosphoglucose, phosphomannose, and phosphoglucosamine isomerases and the pH dependence of the Vmax for some of them in order to separate the enolization and ring opening functions. The active site of rabbit muscle pyruvate kinase will be studied with bromopyruvate; the nature of the reactive nucleophile and the sequence in the area will be determined. Studies on the secondary alpha-H3 isotope effect in the reactions of pyruvate carboxylase and citrate synthase will indicate whether an enolization occurs in the mechanism.