EVIDENCE IN FAVOR OF THE EXISTENCE OF A KINETIC BARRIER FOR PROTON-TRANSFER FROM A SURFACE OF BILAYER PHOSPHOLIPID MEMBRANE TO BULK WATER

When the hydrogen-ion flux is induced by nigericin across the planar b ilayer lipid membrane (BLM) with bulk pH values being equal at the opp osite sides of the BLM, formation of a difference in boundary potentia ls (DELTAphi(b)) on the membrane is observed by the method of inner me mbrane field compensation. pH gradients are titrated routinely by the addition of sodium acetate at one side of the membrane. The increase i n buffer concentration (citrate, phosphate, Mes) leads to a decrease i n DELTAphi(b). DELTAphi(b) forms in the presence of phosphatidylserine in the membrane-forming solution only. It is concluded that the stead y-state difference of the hydrogen ion binding to the opposite surface s of the membrane (HIBD) is created under the conditions of equal pH v alues near surfaces of the BLM. The model of the processes implies tha t nigericin transfers proton predominantly from interface to interface while acetate transfers the proton from bulk phase to bulk phase. In the other series of experiments the monensin-mediated formation of the HIBD leads to the formation of an potassium-ion gradient in the prese nce of nigericin. Thus, a possibility of performing a work due to the formation of HIBD is demonstrated. Owing to these properties the hydro gen-ion binding difference can be interpreted in a first approximation as a difference of surface hydrogen-ion concentration at the opposite sides of the membrane, arising due to the existence of a kinetic barr ier for the proton transfer at the membrane interfaces. These findings can be significant for the mechanism of energy transduction in membra ne phosphorylation in mitochondria and chloroplasts.