Os03g0233900
Please input one-sentence summary here.
Annotated Information
Introduction
Hemoglobins (Hbs) with unknown functions have been found in most organisms. A hypothetical role common tomany of them is nitric oxide (NO) scavenging, which is grounded in the established contribution of Hbs to nitric oxide dioxygenase (HbO2 + NO == metHb + NO3-) (NOD) activity in bacterial flavohemoglobins, the effects of blood cell Hb on NO metabolism, and the general reactivity of oxy, deoxy, and ferric hemoglobins with NO. In plants, the NOD function for Hbs is supported by increases in the level of Hb expression in response to nitrate, nitrite, and nitric oxide, improvements in NO scavenging ability in plants overexpressing Hb, decreases in the levels of NO-sensitive enzymes in plants with down regulated Hb, and the encouragement of cell growth by cyanobacterial Hb in the presence of high concentrations of reactive nitrogen species.
The metabolism of nitrogen is quite different in autotrophs such as plants and cyanobacteria, which must assimilate nitrogen through the reduction of nitrate under conditions ranging from normoxic to anoxic. In these organisms, nitrate and nitrite can accumulate to very high (millimolar) concentrations,particularly when oxygen concentrations are low.Such conditions are associated with plant Hb upregulation,and thus, reactions of nitrate and nitrite with plant and cyanobacterial Hbs are potentially physiologically significant.
Function
May not function as an oxygen storage or transport protein, but might act as an oxygen sensor or play a role in electron transfer, possibly to a bound oxygen molecule. Has an unusually high affinity for O2 because of a very low dissociation constant.
Rice nsHb1 have hypothetical roles in nitrogen metabolism
The reactions of class 1 rice nonsymbiotic Hb (rice nsHb1) with nitrate and nitrite suggested that these Hbs are not oxygen transporters and have hypothetical roles in nitrogen metabolism. And the deoxyferrous forms of each react rapidly with nitrite to form ferric Hb and ferrous-nitrosyl Hb in a fixed ratio, indicative of the production of nitric oxide from the reduction of nitrite by ferrous Hb.[1]
![" Reaction of rice nsHb1 and SynHb with nitrite. The spectral changes associated with Rice nsHb1 [1]).](/index.php/File:Nshb1.GIF)
Rice nsHb1 could serve as anaerobic nitrite reductases in vivo
Rate constants for nitrite reduction by a ferrous plant hemoglobin (rice nonsymbiotic hemoglobin 1) are more than 10 times faster than those observed for animal hemoglobins. These rate constants, along with the relatively high concentrations of nitrite present during hypoxia, suggest that plant hemoglobins could serve as anaerobic nitrite reductases in vivo .[2]
!["Reactivity of nitrite and nitrate with other forms of rice nsHb1, SynHb, and Mb. (from reference [1])."](/index.php/File:Nshb1_Reactivity.GIF)
Rice nsHb1 catalyze the reduction of hydroxylamine to ammonium
Class 1 rice nonsymbiotic hemoglobin (rice nsHb1) catalyze the reduction of hydroxylamine to ammonium at rates 100−2500 times faster than animal hemoglobins including myoglobin, neuroglobin, cytoglobin, and blood cell hemoglobin. These results support the hypothesis that plant contribute to anaerobic nitrogen metabolism in support of anaerobic respiration and survival during hypoxia.[3]
!["Reaction of deoxyferrous Hbs with HA(from reference [3])"](/index.php/File:Reaction_HA.GIF)
!["Relative rates of hydroxylamine reduction by different Hbs(from reference [3])"](/index.php/File:Hydroxylamine_reduction.GIF)
Expression
Protein names
Recommended name:Non-symbiotic hemoglobin 1; Alternative name(s):ORYsa、 GLB1a、 rHb1
Expressed in coleoptiles, embryos, leaves and roots By flooding and etiolating but not by oxidative, nitrosative or hormonal stresses.
These Hbs are not oxygen transporters and have hypothetical roles in nitrogen metabolism. The deoxyferrous forms of each react rapidly with nitrite to form ferric Hb and ferrous-nitrosyl Hb in a fixed ratio, indicative of the production of nitric oxide from the reduction of nitrite by ferrous Hb.[1]
deoxyferrous rice nsHb1 and SynHb convert HA specifically to ammonium at rates 100−2500 times faster than the animal Hbs. These results complement those of nitrite reduction by rice nsHb1 and SynHb and support the hypothesis that they serve as an alternative means of reducing nitrogen metabolites, recycling NADH produced during anaerobic glycolysis, and continuing ammonium production during hypoxia.[3]
Evolution
Globins are heme proteins, which bind and transport oxygen. This family summarizes a diverse set of homologous protein domains, including: (1) tetrameric vertebrate hemoglobins, which are the major protein component of erythrocytes and transport oxygen in the bloodstream, (2) microorganismal flavohemoglobins, which are linked to C-terminal FAD-dependend reductase domains, (3) homodimeric bacterial hemoglobins, such as from Vitreoscilla, (4) plant leghemoglobins (symbiotic hemoglobins, involved in nitrogen metabolism in plant rhizomes), (5) plant non-symbiotic hexacoordinate globins and hexacoordinate globins from bacteria and animals, such as neuroglobin, (6) invertebrate hemoglobins, which may occur in tandem-repeat arrangements, and (7) monomeric myoglobins found in animal muscle tissue.
cd01040: globin [1]
Labs working on this gene
Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, United States
Department of Biochemistry, The George W. Beadle Center, University of Nebraska-Lincoln, USA
References
- ↑ 1.0 1.1 1.2 1.3 1. Plant and cyanobacterial hemoglobins reduce nitrite to nitric oxide under anoxic conditions. Sturms R, et al. Biochemistry, 2011 May 17. PMID 21495624
- ↑ 2. Role of phenylalanine B10 in plant nonsymbiotic hemoglobins. Smagghe BJ, et al. Biochemistry, 2006 Aug 15. PMID 16893175
- ↑ 3.0 3.1 3.2 3.3 3. Hydroxylamine reduction to ammonium by plant and cyanobacterial hemoglobins. Sturms R, et al. Biochemistry, 2011 Dec 20. PMID 22080728
