Photoreaction of Manganese Catalyst in Photosynthetic Oxygen Evolution

Abstract

proper is close to 1; (3) Photoinhibition of the activation-photoreactivation ocours most effectively in weak intensities (<one-fiftieth photosynthetic saturation in normal cells). Apparently at higher intensities an inhibitory photoprocess is overriding. This inhibition proved reversible. The tphotoreactivation leads to new stable 0, evolving centers as evidenced by an increase in the rate at saturating intensity, quantum yield, and the 0, gush.

Changes in Protein Composition and Mn Abundance in Photosystem II Particles on Photoactivation of the Latent O2-Evolving System in Flash-Grown Wheat Leaves

“…The process can be driven by continuous light or by a series of short (as) flashes with intervals of a few seconds, indicative of the involvewr Xnt of a multiquantum process (6,7,11). Through the early and comprehensive studies by Cheniae and Martin (4)(5)(6)(7), the phenomenon was characterized as light-driven incorporation of Mn atoms into 02-evolving system in thylakoid membranes.…”

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

“…As to the role of electron transport in photoactivation, it has been inferred that photoactivation requires some oxidized equivalents on the oxidizing side of PSII, based on the observation that the photoactivation in algal cells and intact leaves was sensitive to DCMU (3,10). From this point of view, the inhibitory effect of N02 and MV shown in the present study seems remarkable in that the generation of wateroxidation activity was affected under the condition which allowed electron transport through both photosystems to accumulate oxidizing equivalents on the oxidizing side of PSII.…”

Energy Capture in Photosynthesis: Photosystem II

“…It appears to be a multiquantu m process of low overall efficiency which is rate saturated in very weak light (189). Analysis of data obtained in flashing light (190) yicldcd as a minimal hypothcsis a mechanism containing two light-driven steps as shown in equation 3 (191) Mn + E ~-MnE ~ MnE' -~ MnEact 3. '…”

“…In vivo the process has been demonstrated in algae (blue-green as well as green) that were 1. grown in darkness (192) or in Mn-free medium (189), extracted with NH2OH (187), and 3. depleted by aging (193) or prolonged anaerobiosis (188). Photoactivation thus seems to be a universal process in the development of the O z evolving apparatus.…”