Hydrazobenzene oxidation by 2,6-dichlorophenol-indophenol in a photoreaction catalyzed by System I of photosynthesis. Hydrazine compounds as donors for Photosystem II

Abstract

1. The kinetics of the photooxidation of hydrazobenzene with dichlorophenol (DCIP), methylviologen and NADP + as electron acceptors were studied in spinach chloroplasts, Tris-treated chloroplasts and System I and II particles, in the presence and absence of dichlorophenyldimethylurea (DCMU). The hydrazobenzene-DCIP photoreaction was much less inhibited by DCMU than the reactions with the other acceptors. 2. For chloroplasts the action spectrum of the quantum yield for the hydrazobenzene-DCIP redox reaction showed a maximum at 710 nm, indicating System I participation. Three or more electrons were transported per quantum absorbed at 700 nm. 3. It is concluded from these and other experiments that hydrazobenzene can be oxidized in at least two photoreactions. In the first place it acts as an efficient donor for System II. This reaction is inhibited by 5 μM DCMU. A second hydrazobenzene-DCIP reaction, which is not inhibited by DCMU, is presumably catalyzed via an oxidized component of the redox chain between Q and System I. 4. Effects of hydrazobenzene on fluorescence and luminescence of chlorophyll a 2 (the chlorophyll a of System II), carotenoid bleaching, and cytochrome b 559 oxidation of System II particles can be explained by the efficient electron donation to System II. 5. N, N′-Phtaloylhydrazine and dichlorophenylhydrazine were found to be relatively efficient donors to System II, although less efficient than hydrazobenzene. The redox reactions with DCIP were inhibited by DCMU.