Abstract
We have previously reported that bacterial flavohemoglobin (HMP) catalyzes both a rapid reaction of heme-bound O2 with nitric oxide (NO) to form nitrate [HMP-Fe(II)O2 + 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 O2 concentrations. It has been alternatively suggested that HMP activity is inhibited at low pO2 because the enzyme is then in the relatively inactive nitrosyl form [koff/kon for NO (0.000008 μM) ≪ koff/kon for O2 (0.012 μM) and KM for O2 = 30-100 μM]. To resolve this discrepancy, we have directly measured heme-ligand turnover and NADH consumption under various O2/NO concentrations. We find that, at biologically relevant O2 concentrations, HMP preferentially binds NO (not O2), which it then reacts with oxygen to form nitrate (in essence NO- + O2 → 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.
| Original language | English |
|---|---|
| Pages (from-to) | 10108-10112 |
| Number of pages | 5 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Volume | 98 |
| Issue number | 18 |
| DOIs | |
| Publication status | Published - 28 Aug 2001 |
| Externally published | Yes |
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ASJC Scopus subject areas
- Genetics
- General
Cite this
Flavohemoglobin denitrosylase catalyzes the reaction of a nitroxyl equivalent with molecular oxygen. / Hausladen, Alfred; Gow, Andrew; Stamler, Jonathan S.
In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 98, No. 18, 28.08.2001, p. 10108-10112.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Flavohemoglobin denitrosylase catalyzes the reaction of a nitroxyl equivalent with molecular oxygen
AU - Hausladen, Alfred
AU - Gow, Andrew
AU - Stamler, Jonathan S.
PY - 2001/8/28
Y1 - 2001/8/28
N2 - We have previously reported that bacterial flavohemoglobin (HMP) catalyzes both a rapid reaction of heme-bound O2 with nitric oxide (NO) to form nitrate [HMP-Fe(II)O2 + 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 O2 concentrations. It has been alternatively suggested that HMP activity is inhibited at low pO2 because the enzyme is then in the relatively inactive nitrosyl form [koff/kon for NO (0.000008 μM) ≪ koff/kon for O2 (0.012 μM) and KM for O2 = 30-100 μM]. To resolve this discrepancy, we have directly measured heme-ligand turnover and NADH consumption under various O2/NO concentrations. We find that, at biologically relevant O2 concentrations, HMP preferentially binds NO (not O2), which it then reacts with oxygen to form nitrate (in essence NO- + O2 → 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.
AB - We have previously reported that bacterial flavohemoglobin (HMP) catalyzes both a rapid reaction of heme-bound O2 with nitric oxide (NO) to form nitrate [HMP-Fe(II)O2 + 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 O2 concentrations. It has been alternatively suggested that HMP activity is inhibited at low pO2 because the enzyme is then in the relatively inactive nitrosyl form [koff/kon for NO (0.000008 μM) ≪ koff/kon for O2 (0.012 μM) and KM for O2 = 30-100 μM]. To resolve this discrepancy, we have directly measured heme-ligand turnover and NADH consumption under various O2/NO concentrations. We find that, at biologically relevant O2 concentrations, HMP preferentially binds NO (not O2), which it then reacts with oxygen to form nitrate (in essence NO- + O2 → 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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U2 - 10.1073/pnas.181199698
DO - 10.1073/pnas.181199698
M3 - Article
VL - 98
SP - 10108
EP - 10112
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
SN - 0027-8424
IS - 18
ER -