Involvement of vertebrate hemoglobin in antioxidant protection: chicken blood as a model

Abstract

Redox balance can be described as the equilibrium between oxidative and reductive forces within the cell. These forces control several cellular events, including the modulation of redox-sensitive receptors and signaling pathways. In cells, glutathione is the major non-protein thiol and is considered the main redox buffer. The ratio between the oxidized (GSSG) and reduced (GSH) forms reflects the cellular redox balance. Reactive protein thiols, including vertebrate hemoglobin (Hb), have been proposed as effective antioxidants that can contribute to the redox balance. To further explore this possibility, chicken ( Gallus gallus (L., 1758)) blood was used as a model system. The use of known oxidants (hydroperoxides, diamide, and a system generating reactive oxygen species) originated a pattern of glutathiolation in chicken erythrocytes that was fully reversed after removal of the oxidant, this being consistent with a physiological response. The glutathiolation sequence correlates to kinetic data on chicken Hb cysteine reactivity. The major chicken hemoglobin (Hb A) is responsible for most of the glutathiolated protein where the presence of externally positioned and fast-reacting cysteines is a contributing factor. The antioxidant potential of fast-reacting Hb cysteines is in line with the conservation of cysteine residues in Hb stereochemical positions in more than 95% of the available avian Hb sequences. This may represent an evolutionary trend for the antioxidant function of externally positioned and reactive cysteines in abundant proteins.