Primary charge separation in photosystem II involves two electrogenic steps

Abstract

Similarities in the piginent and subunit composition and sequence homologies suggest a common evolutionary origin for the reaction centers (RCs) of photosynthetic purple bacteria and photosystem II (PS II) of green plants [1]. Besides these similarities, significant functional differences exist that make comparative studies between both types of RCs interesting. We report here (i) on the electric detection of two kinetically distinct phases of the primary charge separation in PS II with 100 and 500 ps reflecting trapping and charge stabilization, and (ii) the determination of the dielectrically weighted transmembrane distances between the primary donor (P), the pheophytin intermediary acceptor (I), and the first quinoic acceptor (QA). These data are compared with those for purple bacteria. In PS II the reduction of QA is 2–3-times slower, although the dielectric distance between I and Q A appears to be significantly shorter than in purple bacteria.