Limited access of nucleotides to the active site of ATP synthetase during photophosphorylation

Studies on steady state kinetics of enzymes bound to energy-transducing membranes have generally tacitly assumed that their kinetic behavior does not depart greatly from that of enzymes in free solution. However, the microenvironment of these membranes, upon which electrochemical changes occur during catalysis, should be different than an ideal aqueous solution which allows rapid diffusion of solutes. Since different kinetic principles apply to enzymes immobilized on solid supports, due to impaired translocation of reactants near the support (Engasser, Horvath, 1976), the macroscopic behavior of such enzymes does not necessarily reflect intrinsic properties relevant to the molecular mechanism of catalysis (conformational changes, site-site cooperativity, etc.).