ROLE OF MG2+ IONS IN SUBUNIT STRUCTURE AND MEMBRANE BINDING PROPERTIES OF BACTERIAL ENERGY TRANSDUCING ATPASE

ATPase extracted from Streptococcus faecalis membranes was purified by preparative slab gel electrophoresis in the presence of Mg2+ (plus Mg2+ ATPase) and without Mg2+ (minus Mg2+ ATPase). The subunit composition and membrane binding capacity of both preparations was then examined. The plus Mg2+ ATPase had 5 types of subunits (.alpha..beta..gamma..delta..epsilon.) and reattached normally to depleted membranes. The minus Mg2+ ATPase had the .alpha..beta..gamma. and .epsilon. chains, but not .delta. chain, and failed to reattach to membranes. Mg2+ or a similar cationic ligand may anchor the .delta. chain to the core enzyme complex and the .delta. chain in turn is apparently needed for membrane attachment. For the plus Mg2+ ATPase the data are consistent with the subunit stoichiometry and arrangement, (.alpha.3.beta.3 .gamma. .epsilon.)-Mg2+)n-(.delta.).