Dipartimento di Chimica Ugo Schiff, Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino, Italy.
J Inorg Biochem. 2012 Apr;109:1-8. doi: 10.1016/j.jinorgbio.2012.01.007. Epub 2012 Jan 27.
Rainbow trout myoglobin (Mb) is characterized by an unusually low affinity for oxygen, having a P(50) of 4.92±0.29 mm Hg at 25 °C which is the highest ever reported for any vertebrate Mb at the same temperature (Helbo and Fago, (2011) Am. J. Physiol. Regul. Integr. Comp. Physiol. 300, R101-R108). In order to gain insight into the structural factors of the heme pocket that may be important determinants for this atypical oxygen affinity, we have carried out an electronic absorption and resonance Raman characterization of the ferric and ferrous protein with and without exogenous ligands (O(2), CO, F(-)) and compared the results with those of other Mbs. While the ν(Fe-His) stretch appears at a frequency similar to other vertebrate Mbs, the resonance Raman frequencies of the Fe-ligand stretching modes reveal significant variations in the interaction of iron-bound ligands with distal residues. In particular, the spectroscopic characterization highlights two exceptional properties of rainbow trout Mb, a significantly higher level of reversed heme and reduced hydrogen bonding interactions between ligands and the distal HisE7 residue compared with other Mbs. The weakening of the hydrogen bond interaction is proposed to be the primary cause of the significantly reduced oxygen affinity.
虹鳟肌红蛋白（Mb）的氧亲和力异常低，在 25°C 时的 P(50)为 4.92±0.29mmHg，这是迄今为止在相同温度下报道的任何脊椎动物 Mb 中最高的（Helbo 和 Fago，（2011）Am. J. Physiol. Regul. Integr. Comp. Physiol. 300，R101-R108）。为了深入了解血红素口袋的结构因素，这些因素可能是决定这种非典型氧亲和力的重要因素，我们已经对铁和亚铁蛋白进行了电子吸收和共振拉曼表征，同时存在和不存在外源配体（O(2)、CO、F(-))，并将结果与其他 Mb 进行了比较。虽然 ν(Fe-His)伸展在频率上与其他脊椎动物 Mb 相似，但 Fe-配体伸缩模式的共振拉曼频率显示出铁结合配体与远端残基相互作用的显著变化。特别是，光谱表征突出了虹鳟 Mb 的两个特殊性质，与其他 Mb 相比，其逆转的血红素水平显著升高，配体与远端 HisE7 残基之间的氢键相互作用减弱。氢键相互作用的减弱被认为是氧亲和力显著降低的主要原因。
