title: Anadara ovalis hemoglobins: distinct dissociation and ligand binding characteristics.
abstract: The red cells of the arcid clam Anadara ovalis contain two electrophoretically distinct hemoglobins: Hb Major (Hb Ma) and Hb Minor (Hb Mi). The major component consists of two electrophoretically indistinguishable tetramers each composed of two heterodimers; the minor hemoblogin is a homodimer whose subunits are different from the tetramer. Functionally, Hb Ma has a higher P50, exhibits a concentration dependent oxygen affinity, has significant ligand cooperativity (n = 2.0), lacks a Bohr effect and is unaffected by ATP. HB Mi has a P50 which is lower and independent of hemoglobin concentration, shows appreciable cooperativity (n = 1.4) and exhibits no heterotropic effects. Both Hb Ma and Mi are resistant to dissociation in the presence of 1.0 M NaI, NaCl and guanidine-HCl but dissociate to monomers when converted to the aquamet but not the cyanmet derivative. The dissociation is completely inhibited by mercaptoethanol. The large number of reactive -SH groups (10-13 per tetramer) suggests that the monomerization is mediated by intra-subunit disulfide bridge formation.
mesh_terms: D000818:Animals; D005075:Biological Evolution; D049872:Bivalvia / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D011487:Protein Conformation; D013045:Species Specificity; D014714:Vertebrates / Q000097:blood
chemical_list: D006454:Hemoglobins