The effect of aging on rat liver phosphoglycerate kinase and comparison with the muscle enzyme

Abstract

Pure liver phosphoglycerate kinase (ATP:3-phospho- d-glycerate 1-phosphotransferase, EC 2.7.2.3) from old rats has been found to be an altered enzyme with certain properties which are dissimilar to those of the enzyme obtained from young animals. Stability during storage, sensitivity to heat, response to antiserum and stability during isoelectric focusing differ. Unchanged are molecular weight, specific activity, K m , reactivity of SH groups, blocked N-terminal residue and leucine for the C-terminal residue. Liver phosphoglycerate kinase differs substantially from the muscle enzyme. Among the differences are stability, heat-sensitivity, K m for 3-phosphoglyceric acid, inactivation by urea and response to antiserum. Nonetheless, a number of properties suggest that the liver and muscle enzymes are similar in structure. Both react with antisera prepared to phosphoglycerate kinase from muscle and liver, respeetively. For both enzymes, the N-terminal residue is blocked and the C-terminal amino acid is leucine. The muscle form has been named phosphoglycerate kinase-1 or A. The only previously known isozyme is the testis enzyme, phosphoglycerate kinase-2 or B. We therefore propose that the liver enzyme be known as phosphoglycerate kinase-3 or C.