Presence of an amino acid oxidase in photosystem II of Anacystis nidulans.

Abstract

Membrane fractions from the blue‐green algae Anacystis nidulans can catalyze O2 evolution with ferricyanide as acceptor in the light and the dark oxidation of l‐arginine. The two reactions are both inhibited by o‐phenanthroline, but they respond to certain trivalent, divalent and monovalent cations (like e.g. La3+ or Ca2+ or K+) in different ways. These metals stimulate the Hill reaction with ferricyanide as acceptor, but totally inhibit l‐arginine oxidation. The order of effectiveness is M3+ > M2+ > M+. The effect of e.g. Ca2+ on the dark oxidation of l‐arginine mirrors the effect of Ca2+ on the light‐driven O2 evolution with ferricyanide, as though these two activities are mutually exclusive, i.e. one process is inhibited to the extent that the other is activated. The enzyme responsible for the dark oxidation of l‐arginine has been purified from A. nidulans and shown to be a flavo‐enzyme [Pistorius, E. K. and Voss, H. (1980) Biochim. Biophys. Acta, 611, 227–240].Active photosystem II particles have also been isolated from Anacystis membrane fractions. They can catalyze 2,6‐dichloroindophenol reduction with diphenylcarbazide as donor in the light. They retain l‐arginine oxidation activity in the presence of EDTA. Both reactions are inhibited by o‐phenanthroline. Moreover, it could be shown that one of the protein bands which has been shown to be characteristic for photosystem II particles [Koenig, F. and Vernon, L. P. (1981) Z. Naturforsch. C36, 295–304], co‐chromatographs with the purified l‐amino‐acid oxidase on SDS gels. An antibody prepared to the purified l‐amino‐acid oxidase also gave a precipitin line with detergent‐treated photosystem II particles.The experiments show that the l‐amino‐acid oxidase is part of photosystem II particles in A. nidulans. This protein might have a dual role: acting as an electron transferring protein in photosynthesis in the presence of certain metal ions (M3+ > M2+ > M+) and as an l‐amino‐acid oxidase in the absence of these.