Altered phosphoglycerate kinase from old rat muscle shows no change in primary structure

Phosphoglycerate kinase (ATP:3-phospho-D-glycerate 1-phosphotransferase, EC 2.7.2.3) from young and old rat muscle was purified to homogeneity. After ascertaining that each preparation of the enzyme obtained from the latter indeed possessed altered properties, matched pairs of young and old enzymes were subjected to amino acid analysis and peptide mapping by HPLC. Following S-carboxymethylation, the respective young and old enzymes were digested with each of the following three proteinases: trypsin, chymotrypsin and S. aureus V8 proteinase. The corresponding peptides were resolved by reverse-phase HPLC. The peptide patterns obtained from both enzyme forms were identical. Even when the peptides obtained from digestion of phosphoglycerate kinase with S. aureus V8 proteinase were further digested with trypsin, no differences were observed. Comparative amino acid analyses also showed no differences. These results provide direct evidence that there are no changes in the sequence of altered rat muscle phosphoglycerate kinase and support the hypothesis that the differences in properties between the young and old forms of the enzyme result from a conformational modification.