Altered phosphoglycerate kinase in aging rats.

Pure phosphoglycerate kinase from young and old rat muscle shows substantial differences in properties. Compared to the "young" enzyme, phosphoglycerate kinase isolated from old animals possesses a greater stability to heat and storage, a slower reacting -SH group, an altered UV spectrum, and requires more antiserum prepared to "young" enzyme for 50% inactivation. Km and specific activity are unchanged. Immunotitration experiments show evidence for an age-related alteration of the enzyme in liver and brain, but not in kidney, lung, or heart. Loss of NH2- or COOH-terminal amino acids is not responsible for the observed differences in the properties of "young" and "old" muscle phosphoglycerate kinase. Both forms of the enzyme contain a blocked (presumably acylated) NH2-terminal residue and the sequence of the three COOH-terminal residues (Ala-Val-Leu-COOH) is identical. Moreover, isoelectric focusing of the two enzyme forms of both acrylamide gels and in a sucrose gradient failed to detect evidence of deamidation or other charge-altering differences. We conclude that, like enolase from aged nematodes, muscle phosphoglycerate kinase becomes altered in conformation in old rats.