Utschig L M, Ohigashi Y, Thurnauer M C, Tiede D M
Chemistry Division, Argonne National Laboratory, Illinois 60439, USA.
Biochemistry. 1998 Jun 9;37(23):8278-81. doi: 10.1021/bi980395n.
Isolated reaction centers (RCs) from Rhodobacter sphaeroides were found to bind Zn(II) stoichiometrically and reversibly in addition to the 1 equiv of non-heme Fe(II). Metal and EPR analyses confirm that Zn(II) is ligated to a binding site that is distinct from the Fe site. When Zn(II) is bound to this site, electron transfer between the quinones QA and QB (QA-QB --> QAQB-) is slowed and the room-temperature kinetics become distributed across the microsecond to millisecond time domain. This effect of metal binding on the kinetics is similar to the more global effect of cooling RCs to 2 degreesC in the absence of Zn(II). This suggests that Zn(II) binding alters localized protein motions that are necessary for rapid QA-QB --> QAQB- electron transfer. Inspection of the RC crystal structure suggests a cluster of histidine ligands located beneath the QB binding pocket as a potential binding site.
人们发现，来自球形红杆菌的分离反应中心（RCs）除了结合1当量的非血红素铁（II）外，还能以化学计量比可逆地结合锌（II）。金属和电子顺磁共振分析证实，锌（II）与一个不同于铁位点的结合位点相连。当锌（II）结合到该位点时，醌QA和QB之间的电子转移（QA-QB→QAQB-）会减慢，室温动力学分布在微秒到毫秒的时间域内。金属结合对动力学的这种影响类似于在没有锌（II）的情况下将反应中心冷却到2℃时更全面的影响。这表明锌（II）的结合改变了局部蛋白质运动，而这种运动是快速的QA-QB→QAQB-电子转移所必需的。对反应中心晶体结构的检查表明，位于QB结合口袋下方的一组组氨酸配体是一个潜在的结合位点。
