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Structural and functional properties of class 1 plant hemoglobins
Author(s) -
Igamberdiev Abir U.,
Bykova Natalia V.,
Hill Robert D.
Publication year - 2011
Publication title -
iubmb life
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.132
H-Index - 113
eISSN - 1521-6551
pISSN - 1521-6543
DOI - 10.1002/iub.439
Subject(s) - chemistry , hexacoordinate , heme , methemoglobin , hemoglobin , cysteine , hemeprotein , oxygen transport , autoxidation , nitrite reductase , electron transport chain , oxygen , stereochemistry , biochemistry , enzyme , nitrate reductase , organic chemistry , silicon
Nonsymbiotic class 1 plant hemoglobins are induced under hypoxia. Structurally they are protein dimers consisting of two identical subunits, each containing heme iron in a weak hexacoordinate state. The weak hexacoordination of heme‐iron binding to the distal histidine results in an extremely high avidity to oxygen, with a dissociation constant in the nanomolar range. This low dissociation constant is due to rapid oxygen binding resulting in protein conformational changes that slow dissociation from the heme site. Class 1 hemoglobins are characterized by an increased rate of Fe 3+ reduction which is likely mediated by cysteine residue. This cysteine can form a reversible covalent bond between two monomers as shown by mass spectrometry analysis and, in addition to its structural role, prevents the molecule from autoxidation. The structural properties of class 1 hemoglobins allow them to serve as soluble electron transport proteins in the enzymatic system scavenging nitric oxide produced in low oxygen via reduction of nitrite. During oxygenation of nitric oxide to nitrate, oxidized ferric hemoglobin is formed (methemoglobin), which can be reduced by an associated reductase. The identified candidate for this reduction is monodehydroascorbate reductase. It is suggested that hemoglobin functions as a terminal electron acceptor during the hypoxic turnover of nitrogen, the process aided by its extremely high affinity for oxygen. © 2011 IUBMB IUBMB Life, 63(3): 146–152, 2011