Effects of Hydroxylamine on Photosystem II

Abstract

The inactivation of O2evolving centers by NH2OH extraction was shown to be reversible. This reversal required light and manganese. This light-induced restoration of active Oevolving centers was analyzed using three green algae and the blue-green alga, Anacystis nidulans. The following results were obtained:1. In any given illumination, the time course proved first order, the rate being proportional to the number of inactive 02 evolution centers.2. The action spectrum proved to be identical to that of system II. The process was independent of system I and occurred in Scenedesmus mutant No. 8 devoid of this system.3. The quantum efficiency was optimal over a small range of intensities and declined at both lower and higher intensities.The efficiency was half maximal at either 1 or 10 hits per system II trap per second. (5,7,14). This inhibitor causes destruction of 02 centers in algae as well as isolated chloroplasts. With spinach chloroplasts, the loss of 02 evolution capacity is accompanied by a loss of the manganese we associated with the 02 center (5, 7).In isolated chloroplasts the hydroxylamine-induced inactivation of 02 centers appears to be irreversible. With whole algae, however, the effect can be completely reversed by light after removal of NH2OH (5,6). It appeared that the previously noted photoreversal of the effect of NH2OH "extraction" might be similar to the photoactivation of 02 centers in tissue depleted of Mn by growth (4,8).In

Studies on the Photoactivation of the Water-Oxidizing Enzyme

“…NH20H extracted algae presumably require neither dark preincubation nor protein synthesis for photoactivation (10). The results reported here prompted reexamination ofthe conclusions reached with NH20H extracted algae.…”

“…This multiquantum process has been observed with Mn-deficient algae made Mn-sufficient (9), NH20H extracted algae (10), dark grown Chlorella capable of synthesis in darkness of the pigments of photosynthesis, PSI and PSII trapping centers and electron transport components (1 1), wheat leaves greened under widely spaced flash regimes leading to the synthesis of the pigments of photosynthesis, PSI and PSII trapping centers and electron transport components but not the active water oxidizing S-State complex (22), and Tris-extracted spinach chloroplasts reactivated by DCIPH23 washings (56).…”

“…Here, we report on studies made with NH2OH-extracted wheat leaf segments and Chlamydomonas. Previous studies have shown that photoactivation occurs in several different NH20H extracted algae (10). (30).…”

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

“…NH20H also causes solubilization of Mn and inactivation of the S-state enzyme in isolated chloroplasts [2], algae [2,19] and leaves [18], however, the effect(s) of NH20H on solubilization/perturbation of the PS II extrinsic polypeptides in these systems is unknown. Although photoactivation of the water-oxidizing enzyme has been described for NH20H extracted algae [20] and leaves [18] …”

Photoactivation of the Water-Oxidation System in Isolated Intact Chloroplasts Prepared from Wheat Leaves Grown under Intermittent Flash Illumination

“…In reactivation experiments with whole algal cells, on the other hand, Cheniae and Martin (4) lans with no externally added factor. Similar photoactivation with no external factor is commonly observed for dark-grown algal cells (5), dark-grown gymnosperm leaves (I 1, 15) or for intermittently flashed angiosperm leaves (10,18), when illumination is given to intact cells or leaves before isolation of chloroplasts.…”