Purification and properties of human cataractous lens glyceraldehyde-3-phosphate dehydrogenase.

ABSTRACT

Glyceraldehyde-3-phosphate dehydrogenase has been shown to occur in three different forms in the human adult cataractous lens a membrane bound form (M) and at least two cytosolic isozymes I1 and I2. Similar Km's for substrate, cofactor and HAsO4 were established for each form and all three forms, to differing degree, require a reduced sulfhydryl group for maximum activity. A variety of phosphonucleosides (ATP, ADP, AMP and 3' 5' cyclic AMP) as well as NADH inhibit enzyme activity. Inhibition by ATP is non-competitive whereas cyclic AMP and NADH compete for the cofactor binding site. Chloride ion stimulates and inhibits enzyme activity at low and high concentrations respectively.