Schneebeck M C, Vigil L E, Friedman J M, Chavez M D, Ondrias M R
Department of Chemistry, University of New Mexico, Albuquerque 87131.
Biochemistry. 1993 Feb 9;32(5):1318-23. doi: 10.1021/bi00056a017.
Time-resolved resonance Raman spectroscopy has been employed to monitor geminate heme-CO rebinding in photolyzed HbCO. The excitation frequency was tuned to enhance the scattering from rebound heme sites 20-500 ns subsequent to CO photolysis. The behavior of vFe-C during ligand rebinding has important ramifications concerning heme pocket dynamics of the distinct equilibrium configurations of the six-coordinate heme sites. During the geminate phase of recombination, the Fe-CO bond strengths and configurations of the rebound sites (inferred from the positions and line widths of vFe-C) were found to be the same as those of equilibrium configurations of HbCO within 500 ns of CO photolysis for all samples. No evidence was found for the existence of transient metastable configurations during geminate recombination. Spectra obtained at earlier times (100 ns) revealed small differences in the geminate rebinding rates of the two equilibrium configurations. Since there is little or no further CO rebinding between 100 and 500 ns after photolysis, some interconversion must occur between the dominant HbCO configurations on a submicrosecond time scale.
时间分辨共振拉曼光谱已被用于监测光解的HbCO中双生血红素-CO的重新结合。激发频率被调谐以增强在CO光解后20 - 500纳秒内从重新结合的血红素位点的散射。在配体重新结合过程中，vFe-C的行为对于六配位血红素位点不同平衡构型的血红素口袋动力学具有重要影响。在重新结合的双生阶段，对于所有样品，在CO光解后500纳秒内，重新结合位点的Fe-CO键强度和构型（从vFe-C的位置和线宽推断）被发现与HbCO的平衡构型相同。没有发现双生重新结合过程中存在瞬态亚稳构型的证据。在更早时间（100纳秒）获得的光谱揭示了两种平衡构型的双生重新结合速率存在小的差异。由于在光解后100至500纳秒之间几乎没有或没有进一步的CO重新结合，一些主要的HbCO构型之间必须在亚微秒时间尺度上发生相互转化。
