Electronic Control of Discrimination between O2 and CO in Myoglobin Lacking the Distal Histidine Residue

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• 作者：Ryu Nishimura ; Tomokazu Shibata ; Izumi Ishigami ; Takashi Ogura ; Hulin Tai ; Satoshi Nagao ; Takashi Matsuo ; Shun Hirota ; Osami Shoji ; Yoshihito Watanabe ; Kiyohiro Imai ; Saburo Neya ; Akihiro Suzuki ; Yasuhiko Yamamoto
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：January 21, 2014
• 年：2014
• 卷：53
• 期：2
• 页码：1091-1099
• 全文大小：410K
• ISSN：1520-510X

文摘

We analyzed the oxygen (O₂) and carbon monoxide (CO) binding properties of the H64L mutant of myoglobin reconstituted with chemically modified heme cofactors possessing a heme Fe atom with a variety of electron densities, in order to elucidate the effect of the removal of the distal His64 on the control of both the O₂ affinity and discrimination between O₂ and CO of the protein by the intrinsic heme Fe reactivity through the electron density of the heme Fe atom (蟻_Fe). The study revealed that, as in the case of the native protein, the O₂ affinity of the H64L mutant protein is regulated by the 蟻_Fe value in such a manner that the O₂ affinity of the protein decreases, due to an increase in the O₂ dissociation rate constant, with a decrease in the 蟻_Fe value, and that the O₂ affinities of the mutant and native proteins are affected comparably by a given change in the 蟻_Fe value. On the other hand, the CO affinity of the H64L mutant protein was found to increase, due to a decrease in the CO dissociation rate constant, with a decrease in the 蟻_Fe value, whereas that of the native protein was essentially independent of a change in the 蟻_Fe value. As a result, the regulation of the O₂/CO discrimination in the protein through the 蟻_Fe value is affected by the distal His64. Thus, the study revealed that the electronic tuning of the intrinsic heme Fe reactivity through the 蟻_Fe value plays a vital role in the regulation of the protein function, as the heme environment furnished by the distal His64 does.