Nishiyama Y, Hayashi H, Watanabe T, Murata N
Department of Regulation Biology, National Institute for Basic Biology, Okazaki, Japan.
Plant Physiol. 1994 Aug;105(4):1313-9. doi: 10.1104/pp.105.4.1313.
We investigated the factors responsible for the heat stability of photosynthetic oxygen evolution by examining thylakoid membranes from the cyanobacterium Synechococcus sp. PCC 7002. We found that treatment of the thylakoid membranes with 0.1% Triton X-100 resulted in a remarkable decrease in the heat stability of oxygen evolution, and that the heat stability could be restored by reconstituting the membranes with the components that had been extracted by Triton X-100. The protein responsible for the restoration of heat stability was purified from the Triton X-100 extract by two successive steps of chromatography. The purified protein had a molecular mass of 16 kD and exhibited the spectrophotometric properties of a c-type Cyt with a low redox potential. The dithionite-minus-ascorbate difference spectrum revealed an alpha band maximum at 551 nm. We were able to clone and sequence the gene encoding this Cyt from Synechococcus sp. PCC 7002, based on the partial amino-terminal amino acid sequence. The deduced amino acid sequence revealed a gene product consisting of a 34-residue transit peptide and a mature protein of 136 residues. The mature protein is homologous to Cyt c550, a Cyt with a low redox potential. Thus, our results indicate that Cyt c550 greatly affects the heat stability of oxygen evolution.
我们通过研究蓝藻聚球藻属PCC 7002的类囊体膜，来探究光合放氧热稳定性的影响因素。我们发现，用0.1% Triton X-100处理类囊体膜会导致放氧热稳定性显著下降，且通过用Triton X-100提取的成分重构膜，热稳定性可以恢复。负责恢复热稳定性的蛋白质通过两步连续的层析从Triton X-100提取物中纯化出来。纯化后的蛋白质分子量为16 kD，表现出具有低氧化还原电位的c型细胞色素的分光光度特性。连二亚硫酸盐-抗坏血酸盐差光谱显示在551 nm处有一个α带最大值。基于部分氨基末端氨基酸序列，我们能够从聚球藻属PCC 7002中克隆并测序编码这种细胞色素的基因。推导的氨基酸序列显示一个由34个残基的转运肽和一个136个残基的成熟蛋白组成的基因产物。成熟蛋白与具有低氧化还原电位的细胞色素c550同源。因此，我们的结果表明细胞色素c550极大地影响放氧的热稳定性。
