INDIRECT REDUCTION OF CYTOCHROME B559 IN ISOLATED REACTION CENTERS OFPHOTOSYSTEM-II BY EXOGENOUS FLAVINS

Cytochrome b559 contained within the isolated reaction centre of photo system II can, under anaerobic conditions, be directly reduced by phot oinduced electron transfer from exogenously added flavins. This chloro phyll-independent reaction occurs when glucose oxidase is present. Glu cose oxidase is a flavin-containing enzyme (its prosthetic group being flavin-adenine dinucleotide) and is often used as part of an oxygen t rap together with glucose and catalase. Thus, studies using this chemi cal trap to create anaerobic conditions should take into account the p ossibility of inducing a non-photosynthetic electron transfer process in isolated photosystem II complexes. However, the flavin-catalyzed pr ocess is restricted to excitation with blue light and can be used as a convenient non-chemical method to modify the redox state of cytochrom e b559.