Flavohemoglobin denitrosylase catalyzes the reaction of a nitroxyl equivalent with molecular oxygen

被引:136
作者
Hausladen, A
Gow, A
Stamler, JS [1 ]
机构
[1] Duke Univ, Med Ctr, Dept Med, Durham, NC 27710 USA
[2] Duke Univ, Ctr Med, Howard Hughes Med Inst, Durham, NC 27710 USA
[3] Duke Univ, Ctr Med, Dept Biochem, Durham, NC 27710 USA
关键词
D O I
10.1073/pnas.181199698
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
We have previously reported that bacterial flavohemoglobin (HMP) catalyzes both a rapid reaction of heme-bound O-2 with nitric oxide (NO) to form nitrate [HMP-Fe(II)O-2 + NO --> HMP-Fe(III) + NO3-] and, under anaerobic conditions, a slower reduction of heme-bound NO to an NO- equivalent (followed by the formation of N2O), thereby protecting against nitrosative stress under both aerobic and anaerobic conditions, and rationalizing our finding that NO is rapidly consumed across a wide range Of O-2 concentrations. It has been alternatively suggested that HMP activity is inhibited at low pO(2) because the enzyme is then in the relatively inactive nitrosyl form [k(off)/k(on) for NO (0.000008 muM)) much less than k(off)/k(on) for O-2 (0.012 muM) and K-M for O-2 = 30-100 muM]. To resolve this discrepancy, we have directly measured heme-ligand turnover and NADH consumption under various O-2/NO concentrations. We find that, at biologically relevant O-2 concentrations, HMP preferentially binds NO (not O-2), which it then reacts with oxygen to form nitrate (in essence NO- + O-2 --> NO3-. During steady-state turnover, the enzyme can be found in the ferric (FeIII) state. The formation of a heme-bound nitroxyl equivalent and its subsequent oxidation is a novel enzymatic function, and one that dominates the oxygenase activity under biologically relevant conditions. These data unify the mechanism of HMP/NO interaction with those recently described for the nematode Ascaris and mammalian hemoglobins, and more generally suggest that the peroxidase (FeIII)-like properties of globins have evolved for handling of NO.
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页码:10108 / 10112
页数:5
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