Article

Correlation between hemichrome stability and the root effect in tetrameric hemoglobins.

Department of Chemistry, University of Naples Federico II, Complesso Universitario Monte S. Angelo, Naples, Italy.
Biophysical Journal (impact factor: 3.65). 09/2009; 97(3):866-74. DOI:10.1016/j.bpj.2009.04.056 pp.866-74
Source: PubMed

ABSTRACT Oxidation of Hbs leads to the formation of different forms of Fe(III) that are relevant to a range of biochemical and physiological functions. Here we report a combined EPR/x-ray crystallography study performed at acidic pH on six ferric tetrameric Hbs. Five of the Hbs were isolated from the high-Antarctic notothenioid fishes Trematomus bernacchii, Trematomus newnesi, and Gymnodraco acuticeps, and one was isolated from the sub-Antarctic notothenioid Cottoperca gobio. Our EPR analysis reveals that 1), in all of these Hbs, at acidic pH the aquomet form and two hemichromes coexist; and 2), only in the three Hbs that exhibit the Root effect is a significant amount of the pentacoordinate (5C) high-spin Fe(III) form found. The crystal structure at acidic pH of the ferric form of the Root-effect Hb from T. bernacchii is also reported at 1.7 A resolution. This structure reveals a 5C state of the heme iron for both the alpha- and beta-chains within a T quaternary structure. Altogether, the spectroscopic and crystallographic results indicate that the Root effect and hemichrome stability at acidic pH are correlated in tetrameric Hbs. Furthermore, Antarctic fish Hbs exhibit higher peroxidase activity than mammalian and temperate fish Hbs, suggesting that a partial hemichrome state in tetrameric Hbs, unlike in monomeric Hbs, does not remove the need for protection from peroxide attack, in contrast to previous results from monomeric Hbs.

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Keywords

5C state
 
aquomet form
 
combined EPR/x-ray crystallography study
 
different forms
 
EPR analysis
 
ferric tetrameric Hbs
 
Hbs
 
hemichromes coexist
 
high-Antarctic notothenioid fishes Trematomus bernacchii
 
monomeric Hbs
 
partial hemichrome state
 
physiological functions
 
Root effect
 
Root-effect Hb
 
sub-Antarctic notothenioid Cottoperca gobio
 
T quaternary structure
 
T. bernacchii
 
temperate fish Hbs
 
tetrameric Hbs
 
three Hbs