Collins R F, Flint T D, Holzenburg A, Ford R C
Department of Biochemistry and Applied Molecular Biology, UMIST, Manchester, U.K.
Biochem J. 1996 Oct 15;319 ( Pt 2)(Pt 2):585-9. doi: 10.1042/bj3190585.
Two-dimensional (2D) crystals of photosystem II (PS II) treated with various concentrations of the zero-length crosslinker 1-ethyl-3-(3-dimethylaminopropyl))carbodi-imide (EDC) were analysed by electron microscopy in conjunction with crystallographic image processing. The preparations were characterized by SDS/PAGE and oxygen-evolution measurements, and the effectiveness of cross-linking was monitored by measuring the level of protection afforded against high concentrations of NaCl and CaCl2, which normally remove extrinsic proteins from PS II. We found that low concentrations of EDC (0.25%) increase the order of 2D crystals of PS II. Treatments with EDC concentrations higher than 0.5% did not improve the order of 2D crystals but induced gross structural changes, which were correlated with a decrease in oxygen evolution activity. Structural changes due to cross-linking did not affect packing or symmetry of the 2D crystals, further supporting the conclusion that PS II has a monomeric nature in vivo.
利用电子显微镜结合晶体学图像处理技术，对用不同浓度的零长度交联剂1-乙基-3-(3-二甲基氨基丙基)碳二亚胺（EDC）处理过的光系统II（PS II）二维（2D）晶体进行了分析。通过SDS/PAGE和放氧测量对样品进行了表征，并通过测量高浓度NaCl和CaCl2（它们通常会从PS II中去除外在蛋白）所提供的保护水平来监测交联的有效性。我们发现低浓度的EDC（0.25%）会增加PS II二维晶体的有序性。用高于0.5%的EDC浓度处理并没有改善二维晶体的有序性，反而引发了明显的结构变化，这与放氧活性的降低相关。交联引起的结构变化并未影响二维晶体的堆积或对称性，进一步支持了PS II在体内具有单体性质的结论。
