Lian T, Locke B, Kitagawa T, Nagai M, Hochstrasser R M
Department of Chemistry, University of Pennsylvania, Philadelphia 19104-6323.
Biochemistry. 1993 Jun 8;32(22):5809-14. doi: 10.1021/bi00073a013.
We have undertaken ultrafast infrared (IR) spectroscopic studies in order to elucidate the geometry of bound CO in the alpha and beta subunits of hemoglobin (Hb) M Boston 13CO. Hb M Boston is a mutant human Hb in which the distal histidine in the alpha subunits is replaced by a tyrosine. The IR absorptions of bound 13CO fall at 1925 cm-1 for the alpha subunits and 1907 cm-1 for the beta subunits. Despite a difference of nearly 20 cm-1 in these peaks, the measured anisotropies of the bound 13CO depletions following 30% photolysis are nearly identical, with values of -0.142 +/- 0.002 obtained for the alpha subunits and -0.140 +/- 0.003 obtained for the beta subunits. These translate to values of 20 degrees +/- 1 degree and 21 degrees +/- 1 degree for the values of the average angles between the CO bond and the normal to the heme planes in the alpha and beta subunits, respectively. Our present results and the work of previous investigators [Nagai, M., Yoneyama, Y., & Kitagawa, T. (1991) Biochemistry 30, 6495-6503] suggest that a change in the polar interactions of the bound CO with the heme pocket environment upon substitution of tyrosine for the distal histidine and a less bent structure for the Fe-C-O unit in the alpha subunits are responsible for the difference in the bound CO absorption frequencies in the alpha and beta subunits. A spectrum of the depletion of the bound 13CO peaks following photolysis indicates that both subunits photodissociate CO with the same quantum yield and neither subunit exhibits significant recombination within 1 ns.
我们进行了超快红外（IR）光谱研究，以阐明血红蛋白（Hb）M波士顿13CO的α和β亚基中结合CO的几何结构。Hb M波士顿是一种突变型人类血红蛋白，其中α亚基中的远端组氨酸被酪氨酸取代。结合的13CO的红外吸收在α亚基处为1925 cm-1，在β亚基处为1907 cm-1。尽管这些峰之间相差近20 cm-1，但在30%光解后测得的结合13CO消耗的各向异性几乎相同，α亚基的值为-0.142±0.002，β亚基的值为-0.140±0.003。这分别转化为α和β亚基中CO键与血红素平面法线之间平均角度的值为20°±1°和21°±1°。我们目前的结果以及先前研究人员的工作[Nagai, M., Yoneyama, Y., & Kitagawa, T. (1991) Biochemistry 30, 6495 - 6503]表明，酪氨酸取代远端组氨酸后，结合的CO与血红素口袋环境的极性相互作用发生变化，以及α亚基中Fe - C - O单元的弯曲结构较小，是α和β亚基中结合CO吸收频率差异的原因。光解后结合的13CO峰消耗的光谱表明，两个亚基以相同的量子产率光解离CO，并且在1 ns内两个亚基均未表现出明显的重组。
