Pyocyanine Promoted the Photoreduction of Cytochrome b-559 in Chloroplasts.

A light-induced absorbance increase at 559 nm was observed in spinach chloroplasts in the presence of pyocyanine. The reaction was induced by red light (650 nm) but not by far-red light (720 nm). The light-dark difference spectra indicated that the reduced component was cytochrome b-559. The effect of pyocyanine was nearly saturated at a concentration of 1 &mgr;M and was independent of the transmembrane proton gradient. The pyocyanine-promoted photoreduction of cytochrome b-559 was inhibited by DCMU and DBMIB. In cyanide-poisoned chloroplasts pyocyanine still promoted the photoreduction of cytochrome b-559. In chloroplasts treated with CCCP the oxidation of cytochrome b-559 can be induced by red light of low intensity. Pyocyanine reversed the effects of CCCP so as to promote the reduction of cytochrome b-559 by red light of both high and low intensities. We assumed that pyocyanine affected the light-induced redox reaction of cytochrome b-559 by affecting the protonation of the cytochrome.