ENERGY AND ENTROPY BALANCE OF ATP SYNTHESIS

Analysis of the energy balance at the H+-translocating CF1CF0-ATP synt hase from spinach yields precise data for the H+/ATP coupling ratio an d the standard reaction Gibbs energy, Delta(r)G'(0), of the reaction A DP + P-i --> ATP + H2O. From the temperature dependency of Delta(r)G'( 0) the accompanying Delta(r)H'(0) and Delta(r)S'(0) values are derived . Prerequisite of this analysis is a shift of the reaction quotient fr om values far below 1 for the uncoupled reaction to values near 1 by m eans of the coupling to the energetically downhill translocation of pr otons across the thylakoid membrane. Proton load of the thylakoid lume n is achieved along with the light-induced electron transport. The int ernal pH which is of crucial importance for the energy balance analysi s is obtained from the pH(in)-controlled electron flow rate. Linear re lationships between the logarithm of the reaction quotient and the equ ilibrium transmembrane pH difference prove the reliability of the proc edure. The quantitative results are: (1) H+/ATP = 4.0, independent of pH. (2) Delta(r)G'(0) = 31.3 kJ mol(-1) at conditions of 20 degrees C, pH 8.0, pMg 2.5 and 0.08 M ionic strength. (3) Delta(r)H'(0) = 28.1 k J mol(-1), Delta(r)S'(0) = -11 J K-1 mol(-1). These results are discus sed with regard to the nonuniform data in the literature. (C) 1997 Els evier Science B.V.