Magnesium-Induced Conformational Changes in Na,K-ATPase

Abstract

Publisher Summary This chapter presents evidence for the effects of millimolar Mg 2+ on nucleotide binding and group-specific modifications. The new findings about subunit structure and the stoichiometry of nucleotide binding and phosphorylation are also discussed. The Na, K–ATPase complex from rabbit kidney outer medulla contains two ouabain-sensitive, high-affinity nucleotide binding sites, at which phosphorylation by ATP takes place. Mg 2+ , when binding to capacity regulating sites, induces a conformational change, which gives rise to two additional binding sites. These are ouabain-insensitive, low-affinity, and nonphosphorylating sites. Mg 2+ lowers the affinity of both high-affinity and low-affinity substrate binding, through affinity regulating Mg 2+ sites. Mg 2+ , when binding to affinity regulating and/or capacity regulating sites, has accelerating effects on group-specific modification of arginine, sulfhydryl, and amino groups, located in or near the high-affinity as well as the low-affinity nucleotide binding centers. These findings indicate that Mg 2+ exerts profound conformational changes in the enzyme. Kinetic studies have suggested stimulation by high ATP of the hydrolysis of a presumed K + -dependent, acid-labile phosphointermediate.