Distribution, adaptation and physiological meaning of thiols from vertebrate hemoglobins.
In the present review, the sequences of hemoglobins (Hb) of 267 adult vertebrate species belonging to eight major vertebrate taxa are examined for the presence and location of cysteinyl residues in an attempt at correlation with their ecophysiology. Essentially, all vertebrates have surface cysteinyl residues in Hb molecules whereby their thiol groups may become highly reactive. Thiol-rich Hbs may display eight or more thiols per tetramer. In vertebrates so far examined, the cysteinyl residues occur in 44 different sequence positions in alpha chains and 41 positions in beta chains. Most of them are conservatively located and occur in only a few positions in Teleostei, Aves and Mammalia, whereas they are dispersed in Amphibia. The internal cysteinyl residue alpha104 is ubiquitous in vertebrates. Residue beta93 is highly conserved in reptiles, birds and mammals. The number of cysteine residues per tetramer with solvent access varies in vertebrates, mammalians and bony fish having the lowest number of external residues, whereas nearly all external cysteine residues in Aves and Lepidosauria are of the surface crevice type. In cartilaginous fish, amphibians, Crocodylidae and fresh water turtles, a substantial portion of the solvent accessible thiols are of the totally external type. Recent evidence shows that some Hb thiol groups are highly reactive and undergo extensive and reversible S-thiolation, and that they may be implicated in interorgan redox equilibrium processes. Participation of thiol groups in nitric oxide ((*)NO) metabolism has also been proved. The evidence argues for a new physiologically relevant role for Hb via involvement in free radical and antioxidant metabolism.
Reischl
Evaldo
E
Departamento de Biofísica and Curso de Pós-Graduação em Ciências Biológicas: Fisiologia, Universidade Federal do Rio Grande do Sul, 91501-970 Porto Alegre, RS, Brazil. Electronic address: reisev@yahoo.com.
Dafre
Alcir Luiz
AL
Departamento de Ciências Fisiológicas, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, 8804-900 Florianópolis, SC, Brazil. Electronic address: aldafre@ccb.ufsc.br.
Franco
Jeferson Luis
JL
Departamento de Ciências Fisiológicas, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, 8804-900 Florianópolis, SC, Brazil.
Wilhelm Filho
Danilo
D
Departamento de Ecologia e Zoologia, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil. Electronic address: dawifi@ccb.ufsc.br.
D000222:Adaptation, Physiological / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D008969:Molecular Sequence Data; D013045:Species Specificity; D013438:Sulfhydryl Compounds / Q000737:chemistry / Q000502:physiology*; D014714:Vertebrates / Q000502:physiology*
D006454:Hemoglobins; D013438:Sulfhydryl Compounds; D003545:Cysteine