Hofrichter J, Sommer J H, Henry E R, Eaton W A
Proc Natl Acad Sci U S A. 1983 Apr;80(8):2235-9. doi: 10.1073/pnas.80.8.2235.
A nanosecond absorption spectrometer has been used to measure the optical spectra of hemoglobin between 3 ns and 100 ms after photolysis of the CO complex. The data from a single experiment comprise a surface, defined by the time-ordered set of 50-100 spectra. Singular value decomposition is used to represent the observed spectra in terms of a minimal set of basis spectra and the time course of their amplitudes. Both CO rebinding and conformational changes are found to be multiphasic. Prior to the quaternary structural change, two relaxations are observed that are assigned to geminate recombination followed by a tertiary structural change. These relaxations are interpreted in terms of a kinetic model that points out their potential role in kinetic cooperativity. The rapid escape of CO from the heme pocket compared with the rate of rebinding observed for both R and T quaternary states shows that the quaternary structure controls the overall dissociation rate by changing the rate at which the Fe--CO bond is broken. A comparable description of the control of the overall association rates must await a more complete experimental description of the kinetics of the quaternary T state.
一台纳秒吸收光谱仪被用于测量光解一氧化碳复合物后3纳秒至100毫秒之间血红蛋白的光谱。单次实验的数据构成一个表面，由50 - 100个光谱按时间顺序排列的集合定义。奇异值分解用于根据一组最小的基础光谱及其振幅随时间的变化过程来表示观测到的光谱。发现一氧化碳的重新结合和构象变化都是多相的。在四级结构变化之前，观察到两种弛豫，它们被归因于双生复合，随后是三级结构变化。这些弛豫是根据一个动力学模型来解释的，该模型指出了它们在动力学协同性中的潜在作用。与R态和T态四级结构观测到的重新结合速率相比，一氧化碳从血红素口袋的快速逸出表明，四级结构通过改变铁 - 一氧化碳键断裂的速率来控制整体解离速率。对整体缔合速率控制的类似描述必须等待对四级T态动力学更完整的实验描述。
