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Hell's gate globin I (HGbI) from Methylacidophilum infernorum and related proteins HGbI is a single-domain heme-containing protein isolated from Methylacidiphilum infernorum, an aerobic acidophilic and thermophilic methanotroph. M. infernorum grows optimally at pH 2.0 and 60C and its home is New Zealand's Hell's Gate geothermal park. The physiological role of HGbI has yet to be determined. It has an extremely strong resistance to auto-oxidation, and has fast oxygen-binding/slow release characteristics. Its CO on-rate is comparable to the O2 on-rate, and it is able to bind acetate with high affinity in the ferric state. The coordination of the heme iron changes in the ferrous form from pentacoordinate at low pH to predominantly hexacoordinate at high pH; in the ferric form, it is predominantly hexacoordinate at all pH.
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