The Extrinsic Proteins of an oxygen-evolving Complex in Marine Diatom Cylindrotheca fusiformis

矽藻放氧複合體的膜外蛋白研究

謝國珍(Gow-Jen Shieh) ； 簡麗鳳(Lee-Feng Chien) ； 潘榮隆(Rong-Long Pan)

《Botanical Studies》 52卷2期 (2011/04) Pp. 161-171

摘要

矽藻(Cylindrotheca fusiformis)放氧複合體(oxygen-evolving complex; OEC)的2,6-dichlorophenylindophenol(DCIP)光還原活性（氧氣釋放時的電子傳遞速率）較菠菜低。利用Tris或NaCl沖洗法，得知C. fusiformis的OEC是由位於類囊體表面的兩個分子量為33 kDa及15 kDa膜外蛋白所組成。33kDa蛋白是放氧活性的主要蛋白，因其負責約60% DCIP光還原活性，而15 kDa蛋白約40%。除了C. fusiformis 兩個膜外蛋白之外，發現Ca(上標 2+)、Cl(上標 -)及Mn離子也參與氧氣的釋放。矽藻類囊體氧氣釋放時之Ca(上標 2+)及Cl(上標 -)需求濃度較菠菜高，推測可能是矽藻OEC與Ca(上標 2+)及Cl(上標 -)的結合力較菠菜低。再者，33 kDa及15 kDa兩個膜外蛋白與Ca(上標 2+)之吸附有關，因為當矽藻的類囊體中此兩蛋白被去除時，Ca(上標 2+)含量下降至23%。這兩個蛋白也證實與Mn離子的結合有關。經過胺基酸出現頻率分析之後，確認33 kDa及15kDa蛋白皆為膜外蛋白。

關鍵字

矽藻類囊體 ； 電子傳遞 ； 膜外蛋白 ； 放氧複合體 ； 光還原 ； 光系統II

並列摘要

Diatom Cylindrotheca fusiformis's oxygen-evolving complex (OEC) exhibited much lower 2, 6- dichlorophenylindophenol (DCIP) photoreduction activity (the electron transfer rate during O2 evolution) when compared to that of spinach. The protein composition of the OEC in C. fusiformis diatom thylakoids consist of only two extrinsic proteins with apparent molecular masses of 33 kDa and 15 kDa after Tris or NaCl washing. The 33 kDa protein was mainly responsible for O2 evolving activity and for about 60% of the DCIP photoreduction activity, whereas the 15 kDa protein's photoreduction activity was approximately 40%. Beside the two extrinsic proteins, we found that Ca(superscript 2+), Cl(superscript -) and Mn ions also participate in the O2 evolution of C. fusiformis. The concentrations of Ca(superscript 2+) and Cl(superscript -) required for O2 evolution in diatom thylakoids were higher than those for spinach, suggesting that the binding affinity of Ca(superscript 2+) and Cl(superscript -) in diatom OEC is lower than that of spinach. The 33 kDa and 15 kDa proteins may coincidently function in Ca(superscript 2+) trapping due to a 23% diminishment in content when diatom thylakoids were depleted of both proteins. These two proteins were also involved in the binding of Mn ions. Analysis of amino acid occurrence frequencies confirmed that both 33 kDa and 15 kDa proteins were extrinsic.

並列關鍵字

Diatom thylakoids ； Electron transfer ； Extrinsic proteins ； Oxygen-evolving complex ； Photoreduction ； Photosystem II