The isoelectric point distribution of G-3-P DK and TPI from human lenses was examined as a function of age and cataract formation. Both enzymes exhibited progressive heterogeneity with age ard a shift towards an acidic charge. Little qualitative differences in the pI profiles of G-3-P DH and TPI were found to distinguish mixed cataracts from age comparable normal lenses. While the most alkaline form of G-3-P DH required less HasO4−for optimal activity, or other kinetic property, i.e. Km substrate, cofactor and inhibitors distinguished any of the charge forms of G-3-P DH. All meta-or isozyme forms of TPI had the same Km substrate in the forward and reverse reaction direction. The most acidic forms of G-3-P DH and TPI were less stable to increased temperatures than their more alkaline counterparts suggesting a decreased stability.1. Metazymes are variants of enzymes that are not primarily genetically coded but occur as secondary enzyme modifications (1).