Recent developments in the age-related alteration of enzymes: a review

Recent developments dealing with the age-related alteration of enzymes have been examined. Since the last review of this field, three enzymes have been purified to homogeneity from young and old nematodes (enolase, phosphoglycerate kinase, triosephosphate isomerase) and one from the liver of young and old rats (superoxide dismutase). In all cases except for triosephosphate isomerase, the enzymes from old animals show a reduced catalytic ability compared to those from young animals. In addition, new reports of increases in the amount of altered enzymes in late-passage cells in tissue culture have appeared, though contrary evidence has also been published. The data from these and other papers are compared and discussed. Possible explanations for the alteration of enzymes include error theory, substitution of individual amino acids and conformational change without sequence change. Though final conclusions cannot be made, the evidence favors the latter idea to explain the presence of altered enzymes in old animals.