Preparation and Characterization of Heat-Stable and Very Active Oxygen-Evolving Photosystem II Particles from the Thermophilic Cyanobacterium, Synechococcus elongatu |
| |
Authors: | Ichimura Toshiaki; Miyairi Sachio; Satoh Kazuhiko; Katoh Sakae |
| |
Institution: | 1Department of Biology, Faculty of Science, University of Tokyo Hongo, Tokyo, 113 Japan
2National Chemical Laboratory for Industry Higashi 1-1, Tsukuba, Ibaraki, 305 Japan |
| |
Abstract: | Very active and heat-stable oxygen-evolving photosystem II particleswere isolated from the thermophilic cyanobacterium Synechococcuselongatus by treatment of thylakoid membranes with a non-ionicdetergent, sucrose monolaurate (SML). The particles were analyzedin a comparison with photosystem II particles prepared withß-octylglucoside (OG). The two preparations had similarpolypeptide compositions, which were caracterized by high levelsof polypeptides from phycobilisomes. The ratio of chlorophylla to QA was 45 and there were four Mn atoms and one tightlybound Ca2+ ion per QA in the particles prepared with SML. Thepreparations were thermophilic, showing substantial rates ofoxygen evolution at temperatures up to 60°C. The maximumrates attained at 45°C were as high as 6.0 mmoles O2 mg1Chl h1. PS II particles prepared with OG were similarlythermostable but were less active in oxygen evolution at alltemperatures examined. Kinetic analysis of flash-induced absorptiontransients revealed that about 22% and 28% of photosystem IIreaction centers were not associated with the functional QBsite in the SML- and OG-particles, respectively. When correctedfor the inactive reaction centers, the maximum rates of oxygenevolution by SML- and OG-particles were 7.7 and 7.0 mmoles O2mg1 Chl h1, which correspond to half times of1.9 and 2.1 ms for the first-order electron transfer, respectively.Comparison of these half times with those of the S-state transitionand the release of oxygen indicates that the overall photosystemII electron transport is limited by the reduction of added electronacceptors and not by release of oxygen.
3On leave from National Chemical Laboratory for Industry, Higashi1-1, Tsukuba, Ibaraki 305 |
| |
Keywords: | |
本文献已被 Oxford 等数据库收录! |
|