Characterization of the Light-induced Transient States of the Chlorophyll Proteins 668 and 743 from Atriplex rosea.

The light-induced transient states of chlorophyll-protein 668 (Cp668) and its photoconverted from Cp743 were investigated using flash photolysis. Short lived transient species induced by a short flash were detected in both Cp668 and Cp743. The Cp668 transient had a half decay time of 2.0 milliseconds and showed a broad absorption band at 460 nanometers. The Cp743 transient had a half decay time of only 0.6 millisecond and had a major absorption peak at 410 nanometers in addition, to a broad absorption band around 530 nanometers. Both transient signals were quenched by oxygen. Cp668 had a temperature-dependent delayed fluorescence at room temperature with a half-life of 2.0 milliseconds, the same as the life-time of the absorption transient. This suggests that the transient species observed was a triplet state of chlorophyll.The light-induced transients of both Cp668 and Cp743 were formed with high efficiency. A very low quantum efficiency was found for the photoconversion of Cp668 to Cp743 suggesting another intermediate in the conversion sequence. The photoconversion reaction requires oxygen suggesting that an intermediate in the reaction sequence might be superoxide or singlet oxygen.