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  • Title: Hb Coimbra or alpha 2 beta (2)99(G1)Asp----Glu, a newly discovered highoxygen affinity variant.
    Author: Tamagnini GP, Ribeiro ML, Valente V, Ramachandran M, Wilson JB, Baysal E, Gu LH, Huisman TH.
    Journal: Hemoglobin; 1991; 15(6):487-96. PubMed ID: 1814856.
    Abstract:
    We have identified a new high oxygen affinity hemoglobin variant in members of a Portuguese family; it is characterized by an Asp----Glu replacement at codon 99 of the beta chain which is in the alpha 1 beta 2 interface. The altered functional properties of Hb Coimbra likely result from the inability to form a hydrogen bond between beta 99Glu and alpha 42Tyr; such a bond is formed in deoxy Hb A between the normally occurring beta 99Asp and alpha 42Tyr. The two affected members of the family have a distinct erythrocytosis with hemoglobin levels of 18 to 20 g/dl. The mutation in the beta-globin gene (GAT----GAA at codon 99) resulting in the Asp----Glu replacement is the seventh type at this specific location. A review of the many variants of the alpha and beta chains identifies primarily aspartic acid and glutamic acid residues as being most frequently replaced; it is speculated that codons GAC and GAT (for Asp), and GAG and GAA (for Glu) are most susceptible to mutational events.
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