In vivo inactivation of the yeast plasma membrane ATPase in the absence of exogenous catabolism.

Yeast plasma membrane ATPase is inactivated up to 80% in the absence of catabolism of exogenous nutrients (exogenous catabolism). This inactivation, that is not accompanied by a decrease in the cellular content of ATPase, is due to an irreversible decrease of the Vmax and does not require protein synthesis. The inactivated enzyme maintains the ability to be regulated by fermentable sugars but shows important alterations in the characteristics of this regulation. Upon addition of glucose, the Vmax of the inactivated enzyme increases as well as its Ki for vanadate but, in contrast to the normal enzyme, its affinity for ATP or its pH optimum do not increase. It is concluded that in the absence of exogenous catabolism an irreversible modification of the yeast plasma membrane ATPase takes place that affects several of its kinetic properties.