Photoactivation of NH₂OH‐treated leaves: reassembly of released extrinsic PS II polypeptides and religation of Mn into the polynuclear Mn catalyst of water oxidation

Abstract

Inactivation of the water-oxidizing enzyme by exposure of leaf segments to hydroxylamine results in a disassembly/perturbation of photosystem (PS) II extrinsic polypeptides (17 > 23 kDa) and solubilization of the tetra-Mn complex. Religation of the tetra-Mn complex, reassembly of these PS II extrinsic polypeptides with thylakoid membranes and reappearance of active water-oxidizing activity all require light, and all are unaffected by inhibitors of protein synthesis and photophosphorylation.The results indicate, however, that the reassembly of these PS II extrinsic polypeptides into the multimeric water oxidizing enzyme occurs more rapidly than the photoligation of Mn as the tetra-Mn complex.Photoactivation 0, evolution Manganese

Structural Effects of Cl− and Other Anions on the Water Oxidizing Complex of Chloroplast Photosystem II

“…As postulated for the activating mechanism (8,21,25), those protonations may occur in the cleft holding the Mn cluster. Such a concept would be consistent with the observation that the presence of functional Mn is a prerequisite for the binding of the two small extrinsic polypeptides (3,32,34 The different effectivenesses of Cl-and substituting monovalent anions can be explained by differences of size (2) and hydration energies, which would affect their access to the binding sites, and the binding strength (37). Furthermore, studies of the response of the water oxidizing mechanism to F (13) and investigations of Cl-binding with 35C1-NMR (10) have suggested that the population of binding sites is heterogeneous.…”

Correlations between delayed fluorescence of chlorophyll, metabolism and yield of plants. II. Influence of moisture of leaf and temperature condition on delayed fluorescence of leaves

“…After the separation of chloroplasts from incubation medium content of the obtained weakly associated with membrane polypeptides was 5-6% of the total protein amount in non separated suspension (or 17-20% of membrane whole weakly associated polypeptides). There was also polypeptide of 12-34 kdalton in the separated solution and among them later it was identified 17.2 kdalton thermolabile weakly associated polypeptide of the watersplitting system [24].…”

Studies on the Photoactivation of the Water-Oxidizing Enzyme

“…The acceptor side of PSII was not affected since the rise time of the variable fluorescence measured in the presence or absence of DCMU was increased without altering Fmax or F,) values. Dark preincubation even in the presence of concentrations of CAP and CH sufficient to inhibit protein synthesis abolished susceptibility to photoinhibition and permitted photoactivation of the S-state water oxidizing enzyme and reassembly of the PSII extrinsic polypeptides independent of protein synthesis (3).…”

“…These experiments were performed with NH20H extracted leaf segments from wheat seedlings which had been cultured in [35S042-]containing nutrient medium (see "Materials and Methods"). Leaf segments were incubated in the presence of concentrations of CAP and CH sufficient to inhibit protein synthesis >90% (3). Thus analyses of the effect of photoinhibition on polypeptide abundance (Fig.…”

“…Thus, both proteins may be susceptible to attack by a single protease. We offer the scheme of Figure 11 to explain our conclusions from studies on the disassembly of the S-state complex, the photoinhibition of the oxidant side of PSII traps, the photoinduced recovery of PSII trap function via processes requiring 70S synthesis of a -~34 kD (D2) polypeptide, and the reassembly of the S-state complex via photoactivation (3,4,6) by NH20H or Tris inactivation of the S-state water oxidizing enzyme. We observe solubilization of -4 Mn, 1 to 2 specifically bound Ca2+/PSII units (see, however, Refs.…”