title: Studies on the electron transfer from Tyr-161 of polypeptide D-1 to P680(+) in PS II membrane fragments from spinach.
abstract: The functional connection between redox component Y z identified as Tyr-161 of polypeptide D-1 (Debus et al. 1988) and P680(+) was analyzed by measurements of laser flash induced absorption changes at 830 nm in PS II membrane fragments from spinach. It was found that neither DCMU nor the ADRY agent 2-(3-chloro-4-trifluoromethyl) anilino-3,5-dinitrothiophene (ANT 2p) affects the rate of P680(+) reduction by Y z under conditions where the catalytic site of water oxidation stays in the redox state S1. In contrast to that, a drastic retardation is observed after mild trypsin treatment at pH=6.0. This effect which is stimualted by flash illumination can be largely reversed by Ca(2+). The above mentioned data lead to the following conclusions: (a) the segment of polypeptide D-1 containing Tyr-161 and coordination sites of P680 is not allosterically affected by structural changes due to DCMU binding at the QB-site which is also located in D-1. (b) ANT 2p as a strong protonophoric uncoupler and ADRY agent does not modify the reaction coordinate of P680(+) reduction by Y z , and (c) Ca(2+) could play a functional role for the electronic and vibrational coupling between the redox groups Y z and P680. The electron transport from Y z to P680(+) is discussed within the framework of a nonadiabatic process. Based on thermodynamic considerations the reorganization energy is estimated to be in the order of 0.5 V.
authors.affiliation: Max-Volmer-Institut für Biophysikalische und Physikalische Chemie, Technische Universität Berlin, Straßbe des 17. Juni 135, D 1000, Berlin 12, F.R.G..
authors.forename: G
authors.initials: G
authors.lastname: Renger
authors.forename: H J
authors.initials: HJ
authors.lastname: Eckert
authors.forename: M
authors.initials: M
authors.lastname: Völker