Phenylglyoxal modification of the photosystem II reaction center

Abstract

Time-resolved spectroscopic techniques, including optical flash photolysis and electron spin resonance (ESR), have been used in conjunction with fluorescence-induction and dye-reduction assays to monitor electron transport in Photosystem II (PS II) subchloroplast particles incubated with the covalent modifier, phenylglyoxal. Phenylglyoxal-modified digitonin (D-10) particles from spinach are characterized by (1) a high initial fluorescence yield ( F i) and an abolition of the variable component of fluorescence ( F v); (2) an inhibition of PS-II-mediated reduction of dichlorophenol indophenol (DPIP) by sym-diphenylcarbazide; (3) an abolition of flash-induced absorption transients ( t 1 2 > 2 μ s ) at 820 nm attributed to the primary electron donor, P-680 +; (4) the inhibition of photoreduction of the acceptor Q a; and (5) the elimination of the ESR Signal 2 s and Signal 2 f. These observations suggest the critical participation of specific arginine residues on both the oxidizing and reducing sides of Photosystem II and also implicate phenylglyoxal as a quinone-binding site inhibitor (Golbeck, J.H. and Warden, J.T. (1984) Biochim. Biophys. Acta 767, 263–271).