Kinetic studies on interaction of (Na,K)-ATPase with Cibacron Blue F3GA as probe of the nucleotide fold.

Cibacron Blue F3GA (Cb) effectively and reversibly inhibits the activity of (Na,K)-ATPase. Its inhibitory effect does not occur through occupation of the ouabain binding site, but presumably results from Cb-occupation of one catalytic site not competitively attracting ATP. Cb also inhibits ouabain binding to (Na,K)-ATPase. Its inhibitory effect is competitively antagonized by ATP proving accommodation of Cb in the ATP binding site. - If one admits Cb as a suitable analytical tool for the detection of a supersecondary structure folding pattern, the findings suggest that the ATP binding site is lined by beta-pleated sheets flanked by alpha-helices thus providing an environment that funnels ATP to the catalytic site.