title: pH dependent changes in ADP and ATP affinity for the tight nucleotide-binding site of chloroplast coupling factor 1.
abstract: The pH-dependence of ADP and ATP affinity for CF1 tight nucleotide-binding sites was studied under conditions of equilibrium between bound and free labeled nucleotides. With the nucleotide/CF1 ratio>1, the ATP content in tightly bound nucleotides depended only slightly on medium pH. With the nucleotide/CF1 ratio approaching 1, tightly bound ATP content grew rapidly with decreasing pH. Calculations of ADP/ATP ratio in free and tightly bound nucleotides showed that decreasing the pH from 8.0 to 6.0 induced a 150 times greater affinity of the nucleotide-binding site for ATP than for ADP. The data indicates that ATP-ADP equilibrium at the CF1 tight nucleotide-binding site depends on protonation of specific acid-base groups of the enzyme.
authors.affiliation: The Institute of Soil Science and Photosynthesis, Academy of Science of the USSR, Pushchino, Moscow Region, USSR.
authors.forename: A N
authors.initials: AN
authors.lastname: Malyan
authors.forename: O I
authors.initials: OI
authors.lastname: Vitseva