Abstract
The heat-labilities of liver glucose-6-phosphate dehydro-genase and malic enzyme of 1- and 12-month-old rats were observed by incubation of the crude enzymes at 52 and 55°C, respectively. The biphasic heat-inactivation curves were obtained for those enzymes of the 12-month-olds, whereas no biphasic curves were obtained for the enzymes of the 1-month-olds. The age-dependent rapid inactivations of glucose-6-phosphate dehydrogenase and malic enzyme were not relieved by addition of their substrates in the incubation media. However, the rapid age-dependent inactivations of these enzymes disappeared by addition of NADP. It is suggested that the age-dependent heat-inactivation of these enzymes is ascribed to the conformational modification of the proteins.
