The effects of in vitro ageing on the exopeptidases of human diploid fibroblasts

Abstract

Six exopeptidases present in human diploid fibroblasts were identified by separation on polyacrylamide gel electrophoresis and their activity profiles against 17 dipeptides, two tripeptides and l-leucine -p- nitroanilide determined. No differences in relative activity or in the electrophoretic patterns of any of the six exopeptidases were detected with ageing. Aminoacylarylamidase activity assayed spectrophotometrically showed significantly increased activity in the middle age-group cells as opposed to the enzyme isolated from young and old cells. Heat-inactivation studies using the same substrate suggested the possibility of an increased proportion of heat-labile enzyme in the old cells but interpretation of the data was difficult because of the complex nature of the inactivation curves obtained. Overall, the results tended to refute the hypothesis that age-related changes in the free amino acid pool of human diploid fibroblasts were associated with significant alterations in the activities of cellular exopeptidases.