Biochemical Characterization of the Fungal Plasma Membrane ATPase, An Electrogenic Proton Pump

Abstract

From a variety of flux and electrophysiological studies, it has become clear that there is a rapid and physiologically important circulation of protons across the fungal plasma membrane (Eddy, 1978; Goffeau and Slayman, 1981). Protons are pumped outwards by a primary ATPase, generating both a pH gradient (up to 3 pH units) and a membrane potential (150 to 250 mV, inside negative), and return inwards by way of H⁺-dependent cotransport systems for sugars, amino acids, and inorganic ions (Fig. 1). A major goal of research during the past few years has been to establish the molecular structure of the fungal plasma membrane ATPase. In particular, there has been reason to ask whether it belongs to the F₀F₁ class of mitochondrial, chloroplast, and bacterial ATPases (which are capable of ATP-driven proton translocation, even though they usually function in the opposite direction to synthesize ATP), or whether it is more closely related to the Na⁺/K⁺-ATPase, Ca²⁺-ATPase and H⁺/K⁺-ATPase of animal cells (which act physiologically in the “transport” direction to pump cations across their respective membranes).