Obligatory coupling between proton entry and the synthesis of adenosine 5'-triphosphate in Streptococcus lactis

Abstract

Proton influx was measured after imposition of an electrochemical potential difference for protons (.DELTA..hivin..mu.H+) across the cell membrane of the anaerobe, S. lactis. As .DELTA..hivin..mu.H+ was increased, there was an approximately parallel increase in proton entry, until .DELTA..hivin..mu.H+ attained 175-200 mV. At this point, a new pathway became available for proton entry, allowing an abrupt increase in the rate and extent of H+ influx. This gated response depended upon the value of .DELTA..hivin..mu.H+ itself, and not upon the value of membrane potential or pH gradient. For .DELTA..hivin..mu.H+ above 175 to 200 mV, elevated proton entry occurred only in cells having a functional membrane-bound Ca2+-stimulated, Mg2+-stimulated ATPase (EC 3.6.1.3). When present, elevated proton entry coincided with the appearance of net synthesis of ATP catalyzed by this ATPase. Apparently, membrane-bound ATPase catalyzes an obligatory coupling between the inward movement of protons and synthesis of ATP.