[Role of alkaline phosphatase in the regulation of the stability of glucose-6-phosphate dehydrogenase from human cells cultivated in vitro].

The causes for different stability of glucose-6-phosphate dehydrogenase in two heteroploid cell strains and in the diploid cell strain of human embryo lungs were investigated. The thermostability of glucose-6-phosphate dehydrogenase was shown to be dependent on the coenzyme (NADP) concentration and to be coupled with the activity of alkaline phosphatase. In diploid and heteroploid cell extracts possessing a low alkaline phosphatase activity glucose-6-phosphate dehydrogenase reveals a high stability. In heteroploid cell extracts having a high activity of alkaline phosphatase a fast hydrolysis of NADP and a decrease of glucose-6-phosphate dehydrogenase stability are observed. Inhibition of alkaline phosphatase by levamisole prior to cell disruption does not increase the stability of glucose-6-phosphate dehydrogenase. Presumably destabilization of glucose-6-phosphate dehydrogenase mediated by alkaline phosphatase occurs in intact cells and is an essential mechanism controlling the enzyme activity.