Electrochemical investigation of cyanobacteria Synechococcus sp PCC7942-catalyzed photoreduction of exogenous quinones and photoelectrochemical oxidation of water

The electron transfer from the photosynthetic system in cyanobacteria, Syne chococcus sp. PPC7942 to exogenous electron accepters was examined using se veral electrochemical techniques. 1,4-Benzoquinone (BQ) and 2,6-dimethyl-1, 4-benzoquinone (DMBQ) were found to function as good exogenous electron acc epters for the photosystem. Kinetic analysis with rotating disk amperometry revealed that the photoreduction of these quinones proceeds in Michaelis-M enten type kinetics for the concentration of the quinones and the light int ensity. The electron transfer rate of the BQ reduction was as high as 68% c ompared with that of the photosynthetic oxygen evolution. Synechococcus sp. cell-entrapped and DMBQ-embedded carbon paste electrodes provided steady-s tate current ascribed to the photoelectrochemical oxidation of water. Altho ugh several inhibitors against the photosynthetic system suppressed the pho toelectrochemical response, phenylmercury acetate, which inhibits ferredoxi n and ferredoxin-NADP oxidoreductase, was found to enhance the photocurrent . Some electrochemical aspects of this system are discussed. (C) 2001 Elsev ier Science B.V. All rights reserved.