Abstract
Abstract Electric field induced pH changes of purple membrane suspensions were investigated in the pH range from 4.1 to 7.6 by measuring of the absorbance change of pH indicators. There are, at least, two proton binding sites; one (site 1) releases protons and the other (site 2) takes up protons in the presence of the electric field. The pH dependence of the number of protons released from site 1 and taken up by site 2 indicates that the pK value of site 1 is shifted from 5.0 to 4.6 and that of site 2 from 4.5 to 5.5 by the externally applied electric field of 20 kV/cm. The rate constants of proton binding for site 1 and site 2 in the pH range from 4.7 to 7.3 are estimated to be 2 × 108M−1s−1 and 2 × 107M−1 s−1 respectively.
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