Partial purification and properties of the proton-translocating ATPase of plant plasma membranes

Abstract

The plasma membrane ATPase of plant cells has been postulated to operate as an electrogenic proton pump which derives the co-transport of nutrients with protons and which possibly catalyzes K+ transport (Poole, R. J. (1978) Annu. Rev. Plant Physiol. 29, 437-460). In addition, the enzyme seems to determine cell growth after hormonal stimulation by acidifying the external medium (Marré, E. (1979) Annu. Rev. Plant Physiol. 30, 273-288). In order to substantiate this important physiological role, the ATPase from oat root plasma membranes has been solubilized with a zwitterionic detergent and partially purified. A polypeptide of 93,000 daltons was enriched in the course of the purification. The enzyme was completely specific for ATP as substrate and it was inhibited by vanadate, diethylstilbestrol, and dicyclohexylcarbodiimide but not by oligomycin or ouabain. The ATPase activity was stimulated by K+ but this occurred only at acidic pH and the effect was less than 100%. After reconstitution of proteoliposomes by a freeze-thaw-sonication procedure, proton transport driven by ATP was demonstrated by the quenching of acridine dye fluorescence. Proton transport occurred in the absence of K+ and its electrogenic nature was demonstrated by the requirement for permeant ions (nitrate or K+ with valinomycin). It is suggested that the enzyme is an electrogenic proton pump, somewhat stimulated by K+, but not involved in the transport of this cation.