Characterization of In Vitro Proton Pumping by Microsomal Vesicles Isolated from Corn Coleoptiles

Publisher Website
Google Scholar
Abstract
Corn (Z. mays L. cv. Golden Cross Bantam) coleoptile microsomal vesicles isolated which are capable of ATP-driven H+-transport as measured by [14C]methylamine accumulation and quinacrine fluorescence quenching. Formation of the pH gradient in vitro shows a high specificity for ATP-Mg, is temperature-sensitive, exhibits a pH optimum at 7.5 and is inhibited by carbonyl cyanide m-chlorophenylhydrazone. Of the divalent cations tested, Mn2+ is almost as effective as Mg2+, while Ca2+ is ineffective. Excess divalent cations, particularly Ca2+, reduces the pH gradient. H+ transport is strongly promoted by anions, especially Cl-, while K does not affect pump activity. Studies with 36Cl- indicate that ATP-driven H+ transport into the vesicles is associated with Cl- uptake. Carbonyl cyanide-m-chlorophenylhydrazone and the anion transport inhibitor, 4,4''-diisothiocyano-2,2''-disulfonic acid stilbene, inhibit methylamine accumulation and 36Cl- uptake. Proton pumping is also blocked by diethyl stilbestrol and N,N''-dicyclohexylcarbodiimide, but is insensitive to oligomycin and vanadate. These properties of the pump are inconsistent with either a mitochondrial or plasma membrane origin.