On the current-voltage relationships of energy-transducing membranes: phosphorylating membrane vesicles from Paracoccus denitrificans [proceedings].

The reducing species is actually the unstable semi-reduced dRFIH· radical, which decays spontaneously to an inactive dimer (Massey & Hemmerich, 1978). Thus reduction cannot proceed beyond the stage where the second-order Pd0 reduction becomes slower than the second-order dimerization, and in the dark the solution contains no extra reducing equivalents. On cooling, the Soret band of the cytochrome shifts from 410nm (Fe2+-RH) toward 417 nm (Fe3+-RH, low spin) (Fig. 2). This reversible shift follows perfectly heating ~cool­ ing cycles, and clearly indicates the reverse electron transfer from Fe+ -RH to Pd0 as another possibility of uncoupling. The various possibilities opened by the combination of subzero temperatures and light-activation can be tested on other sites of the cytochrome P-450 cycle and other multi-component electron-transport chains.