PHOSPHORYLATION OF HALF AND ALL SITES IN H+,K+-ATPASE RESULTS IN OPPOSITE CHANGES IN TRYPTOPHAN FLUORESCENCE

The Trp fluorescence increased accompanying phosphorylation by ATP and Acetyl phosphate (AcP) in pig stomach H+, K+-ATPase, respectively, to maximum values of 0.86 and 0.37%. The stoichiometry of the maximum amount of phosphoenzyme formed from ATP, that from AcP, that from inorganic phosphate (P(i)), and the maximum amount of ATP binding to the enzyme was shown to be close to 1:2:2:2. Phosphoenzymes formed were shown to be turning over. The addition of K+ reduced the amount of phosphoenzyme from ATP to one-tenth but reduced those from AcP or P(i) to only the half. The data show that the Trp fluorescence increased with phosphorylation of half of the sites but decreased with phosphorylation of all sites. © 1993 Academic Press, Inc.