Plasma Membrane ATPase of Fungi and Plants as a Novel Type of Proton Pump

Abstract

Publisher Summary This chapter presents the evidence obtained at different levels of biological organization that characterizes the plasma membrane ATPase of fungi and plants as a novel type of proton pump. It presents a parallel discussion of studies with fungal and plant cells to stress the similarities of their bioenergetic mechanisms that plant physiologists and microbial biochemists may have failed to appreciate. The membranes of bacteria, mitochondria, and chloroplasts contain a similar ATPase involved in proton transport. These enzymes are sensitive to azide and dicyclohexylcarbodiimide and, in the case of mitochondria and photosynthetic bacteria, to oligomycin. They do not form phosphorylated intermediates and they have alkaline pH optima and very complicated structures. These enzymes have a hydrophilic catalytic part with five different subunits protruding from the membrane and a hydrophobic part embedded in the membrane with three different subunits that form a proton channel blocked by dicyclohexyl-carbodiimide. A different type of ATPase is found in the microsomes and plasma membranes of animal cells. These enzymes catalyze the exchange of sodium for potassium and of protons for potassium and calcium transport. The ATPase activities are dependent on the presence of the transported cations and the pH optima are neutral.