title: Alteration of enzymes in ageing human fibroblasts in culture. I. Conditions for the appearance of an alteration in glucose 6-phosphate dehydrogenase.
abstract: Glucose 6-phosphate dehydrogenase has been found to be altered in ageing human fibroblasts in culture. In this article, we have studied the effects of incubation conditions on glucose 6-phosphate dehydrogenase present in isolated cells or homogenates from young and old cells. We show that incubation at 4 degrees C and pH 7.4 induced the appearance of a heat-labile enzyme; this was not the case at pH 6.5. Also NADP+, when present, protects the enzyme from being modified. The kinetics of the modification indicates that the altered form of the enzyme is an intermediary stage between the active and inactive forms. We now have a model system in which the appearance of an altered enzyme can be induced in only a few hours; this model will be used in our next paper to study the mechanism of this alteration.
mesh_terms: D002470:Cell Survival; D046508:Culture Techniques; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000201:enzymology*; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D009249:NADP / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D009249:NADP; D005954:Glucosephosphate Dehydrogenase