Purified vacuolar inorganic pyrophosphatase consisting of a 75-kDa polypeptide can pump H+ into reconstituted proteoliposomes.

ABSTRACT

Inorganic pyrophosphatase was purified to homogeneity from the vacuolar membranes of pumpkin hypocotyl tissue. The purified Inorganic pyrophosphatase consists of a single kind of 75-kDa polypeptide, and the stacked molecules with a repeating unit of 5.8 x 3.8 nm are seen under electron micrography. It exhibits H(+)-translocating activity across membranes coupled with PPi hydrolysis when it is reconstituted into proteoliposomes. A monovalent cation is required for the H+ translocation with the K+ ion being the most effective, but evidence for active transport of 42K+ into proteoliposomes was not obtained under the conditions tested. The hydrolysis of PPi by the reconstituted proteoliposomes is stimulated by the addition of a H+ ionophore, carbonyl cyanide p-trifluoromethyoxyphenylhydrazone, but not by a K+ ionophore, valinomycin. Both hydrolysis of PPi and PPi-dependent H+ translocation of the proteoliposomes are inhibited by N,N'-dicyclohexylcarbodiimide.