P700+- and 3P700-induced quenching of the fluorescence at 760 nm in trimeric Photosystem I complexes from the cyanobacterium Arthrospira platensis

A nonlinear relationship between the variable fluorescence around 760 nm and the [P700red]/[P700total] ratio was derived from titration curves of the absorbance change at 826 nm and the variable fluorescence at 760 nm as a function of the redox potential imposed on the sample solution at room temperature before freezing. The result indicates that the energy exchange between the antennae of different monomers within a PS I trimer stimulates quenching of F760 by P700+.