Extended X-ray absorption fine structure of Mn2+ and Mn2+ X ATP complex bound to coupling factor 1 of the H+-ATPase from chloroplasts.

Abstract The spinach chloroplast ATPase, coupling factor 1, contains three tight Mn2+-binding sites which interact cooperatively. The bound manganese coordinations were studied by x-ray absorption fine structure analysis. Mn2+ was found to be bound to the enzyme with an average Mn-O bond length of 2.15 +/- 0.15 A, significantly shorter than the 2.15 +/- 0.15 A of the Mn-O bond of the average first hydration shell for Mn2+ in aqueous solution. On adding ATP to the manganese-enzyme mixture, a tertiary complex of Mn2+ X ATP X enzyme was formed as indicated by the appearance of a second shell. Mn-P bond distances were estimated at 4.95 +/- 0.15 A in the tertiary Mn2+ X ATP X enzyme complex, which was considerably longer than the Mn-P bond distance of 3.36 +/- 0.15 A for the Mn2+ X ATP complex in aqueous solution. The Mn-P bond distance in the tertiary Mn2+ X ATP X enzyme complex decreased to 4.32 +/- 0.15 A when selenite, a potent effector of ATPase activity, was added. Based on these results, it is suggested that the tertiary complex is required for catalysis. The stimulation of ATP hydrolysis by anions such as selenite may be the result of shortening the distance between Mn2+ and the ATP phosphates in the enzyme active site.