Spectral properties of a divinyl chlorophyll a harboring mutant of Synechocystis sp. PCC6803

Abstract

A divinyl chlorophyll (DV-Chl) a harboring mutant of Synechocystis sp. PCC 6803, in which chlorophyll species is replaced from monovinyl(normal)-Chl a to DV-Chl a, was characterized. The efficiency of light utilization for photosynthesis was decreased in the mutant. Absorption spectra at 77K and their fourth derivative analyses revealed that peaks of each chlorophyll forms were blue-shifted by 1-2nm, suggesting lowered stability of chlorophylls at their binding sites. This was also true both in PSI and PSII complexes. On the other hand, fluorescence emission spectra measured at 77K were not different between wild type and the mutant. This indicates that the mode of interaction between chlorophyll and its binding pockets responsible for emitting fluorescence at 77K is not altered in the mutant. P700 difference spectra of thylakoid membranes and PSI complexes showed that the spectrum in Soret region was red-shifted by 7nm in the mutant. This is a characteristic feature of DV-Chl a. Microenvironments of iron-sulfur center of a terminal electron acceptor of PSI complex, P430, were practically the same as that of wild type.