Studies on phosphoglucose isomerase from cultured human fibroblasts: Absence of detectable ageing effects on the enzyme

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Abstract
Some properties of the enzyme phosphoglucose isomerase (PGI) from the foetal lung fibroblast strain MRC‐5 have been investigated throughout the in vitro lifespan of this cell strain. No significant age‐related alterations in specific activity or thermostability of PGI could be detected. Titration of enzymatic activity with antibody directed against purified PGI showed no detectable differences in PGI from extracts of early passage cells compared with enzyme from senescent cells. The effect of p‐fluorophenylalanine incorporation on PGI was examined in early passage fibroblasts. Thermostability studies showed increased heat lability of PGI from analogue treated cells when compared with enzyme from control cells at the same passage. However, no inactive PGI protein could be detected by antiserum titration in extracts from analogue‐treated cells. The results indicate that no significant amount of altered or inactive PGI is produced in ageing fibroblasts.