Sucheta A, Szundi I, Einarsdóttir O
Department of Chemistry and Biochemistry, University of California, Santa Cruz 95064, USA.
Biochemistry. 1998 Dec 22;37(51):17905-14. doi: 10.1021/bi981092w.
The reduction of dioxygen to water by cytochrome c oxidase was monitored in the Soret region following photolysis of the fully reduced CO complex. Time-resolved optical absorption difference spectra collected between 373 and 521 nm were measured at delay times from 50 ns to 50 ms and analyzed using singular value decomposition and multiexponential fitting. Five processes were resolved with apparent lifetimes of 0.9 micros, 8 micros, 36 micros, 103 micros, and 1.2 ms. A mechanism is proposed and spectra of intermediates are extracted and compared to model spectra of the postulated intermediates. The model builds on an earlier mechanism that used data only from the visible region (Sucheta et al. (1997) Biochemistry 36, 554-565) and provides a more complete mechanism that fits results from both spectral regions. Intermediate 3, the ferrous-oxy complex (compound A) decays into a 607 nm species, generally referred to as P, which is converted to a 580 nm ferryl form (Fo) on a significantly faster time scale. The equilibrium constant between P and Fo is 1. We propose that the structure of P is a3(4+)=O CuB2+-OH- with an oxidizing equivalent residing on tyrosine 244, located close to the binuclear center. Upon conversion of P to Fo, cytochrome a donates an electron to the tyrosine radical, forming tyrosinate. Subsequently a proton is taken up by tyrosinate, forming F(I) [a3(4+)=O CuB2+-OH- a3+ CuA+]. This is followed by rapid electron transfer from CuA to cytochrome a to produce F(II) [a3(4+)=O CuB2+-OH- a2+ CuA2+].
在完全还原的一氧化碳复合物光解后，在索雷特区域监测细胞色素c氧化酶将双氧还原为水的过程。在50纳秒至50毫秒的延迟时间下测量了373至521纳米之间收集的时间分辨光吸收差光谱，并使用奇异值分解和多指数拟合进行分析。分辨出了五个过程，其表观寿命分别为0.9微秒、8微秒、36微秒、103微秒和1.2毫秒。提出了一种机制，提取了中间体的光谱，并与假定中间体的模型光谱进行了比较。该模型基于早期的一种机制，该机制仅使用了来自可见光区域的数据（苏切塔等人，《生物化学》，1997年，第36卷，第554 - 565页），并提供了一种更完整的机制，该机制符合两个光谱区域的结果。中间体3，即亚铁 - 氧复合物（化合物A）衰变为一种607纳米的物质，通常称为P，其在明显更快的时间尺度上转化为580纳米的高铁形式（Fo）。P和Fo之间的平衡常数为1。我们提出P的结构是a3(4 +)=O CuB2 + - OH - ，氧化当量位于靠近双核中心的酪氨酸244上。在P转化为Fo时，细胞色素a将一个电子捐赠给酪氨酸自由基，形成酪氨酸盐。随后质子被酪氨酸盐吸收，形成F(I) [a3(4 +)=O CuB2 + - OH - a3 + CuA +]。接着是电子从CuA快速转移到细胞色素a，产生F(II) [a3(4 +)=O CuB2 + - OH - a2 + CuA2 +]。
