STOICHIOMETRY OF PIGMENTS AND RADICAL PAIR FORMATION UNDER SATURATINGPULSE EXCITATION IN D1 D2/CYTB(559) PREPARATIONS/

Chlorophyll a content and maximum yield of radical ion pair formation, P680(+.)Pheo(-.), were analyzed in D1/D2/cytb(559) preparations isola ted from spinach. The following results were obtained: (a) chromatogra phic analysis with HPLC using an area-ratio method independent of exti nction coefficients revealed that 7 +/- 0.5 Chl a are present per 2 Ph eo; (b) based on highly sensitive silver staining of proteins and its densitometric evaluation, the contamination by CP47 was estimated to b e 4%, i.e., no more than 0.8 Chl can be ascribed to this Chl a binding protein; (c) measurements of laser flash induced absorption changes a t 830 nm as a function of the pulse energy indicate that under light s aturating conditions one P680(+.)Pheo(-.) radical pair can be formed p er 7-8 Chl a; (d) based on the saturation behavior of the different de cay components of the absorption changes and on a comparison of the ab sorption and single photon counting fluorescence data, the 5-ns compon ent is inferred to originate from 'disconnected' Chi. These results le ad to the conclusion that functionally fully competent D1/D2/cytb(559) complexes contain 6 Chl per 2 Pheo. More than 90% of the centres are able to perform a charge separation leading to the radical pair P680(.)Pheo(-.).