Farver O, Shahak Y, Pecht I
Biochemistry. 1982 Apr 13;21(8):1885-90. doi: 10.1021/bi00537a028.
French bean plastocyanin is stoichiometrically and specifically labeled upon reduction by Cr(II)aq ions, yielding a substitution-inert (Cr(III) adduct at the protein surface. The effect of the modification on the activity of plastocyanin in electron transfer between photosystems II and I has been investigated. The photoreduction and photooxidation by chloroplasts or by photosystem I reaction centers, respectively, chloroplasts or by photosystem I reaction centers, respectively, of native and Cr(III)-labeled plastocyanin have been compared. It was found that whereas the photoreduction rates of native and Cr-labeled plastocyanin were indistinguishable, the rates of photooxidation of the modified protein were markedly attenuated relative to those of the native one. This difference in reactivity clearly reflects the perturbation of the electron transfer pathway to P700. These findings, in conjunction with the structure of plastocyanin and the locus of CR(III) binding on its surface, lead to the following interpretation: (a) There are most probably two physiologically significant, electron transfer sites on plastocyanin. (b) The site involved in the electron transfer to P700 is most likely in the region of tyrosine-83 and the negatively charged patch proximal to it. By elimination we assume that the second site is centered at the hydrophobic region of histidine-87.
菜豆质体蓝素在被水合Cr(II)离子还原时会按化学计量比且特异性地被标记，在蛋白质表面产生一种取代惰性的（Cr(III)加合物）。已经研究了这种修饰对质体蓝素在光系统II和I之间电子转移活性的影响。分别比较了天然质体蓝素和Cr(III)标记的质体蓝素被叶绿体或光系统I反应中心进行光还原和光氧化的情况。结果发现，虽然天然质体蓝素和Cr标记的质体蓝素的光还原速率没有区别，但修饰后蛋白质的光氧化速率相对于天然蛋白质明显减弱。这种反应性的差异清楚地反映了电子传递途径对P700的扰动。这些发现，结合质体蓝素的结构及其表面上Cr(III)结合的位点，得出以下解释：(a)质体蓝素上很可能有两个具有生理意义的电子传递位点。(b)参与向P700电子传递的位点很可能在酪氨酸-83及其附近带负电荷区域。通过排除法，我们假设第二个位点以组氨酸-87的疏水区域为中心。
