George G N, Prince R C, Cramer S P
EXXON Research and Engineering Company, Annandale, NJ 08801.
Science. 1989 Feb 10;243(4892):789-91. doi: 10.1126/science.2916124.
As the originator of the oxygen in our atmosphere, the photosynthetic water-splitting enzyme of chloroplasts is vital for aerobic life on the earth. It has a manganese cluster at its active site, but it is poorly understood at the molecular level. Polarized synchrotron radiation was used to examine the x-ray absorption of manganese in oriented chloroplasts. The manganese site, in the "resting" (S1) state, is an asymmetric cluster, which probably contains four manganese atoms, with interatomic separations of 2.7 and 3.3 angstroms; the vector formed by the 3.3-angstrom manganese pair is oriented perpendicular to the membrane plane. Comparisons with model compounds suggest that the cluster contains bridging oxide or hydroxide ligands connecting the manganese atoms, perhaps with carboxylate bridges connecting the 3.3-angstrom manganese pair.
作为地球大气中氧气的来源，叶绿体的光合水裂解酶对地球上的需氧生命至关重要。其活性位点有一个锰簇，但在分子水平上人们对它了解甚少。利用偏振同步辐射来检测定向叶绿体中锰的X射线吸收。处于“静止”（S1）状态的锰位点是一个不对称簇，可能包含四个锰原子，原子间间距为2.7埃和3.3埃；由3.3埃锰对形成的向量垂直于膜平面。与模型化合物的比较表明，该簇含有连接锰原子的桥连氧化物或氢氧化物配体，或许还有连接3.3埃锰对的羧酸盐桥。
