The Kinetics of Ligand Binding and of the Association-Dissociation Reactions of Human Hemoglobin

摘要: Abstract Dissociation of both human deoxyhemoglobin (deoxy-Hb) and carboxyhemoglobin (HbCO) at alkaline pH exposes previously buried tyrosine residues to the environment alters their pK. Subunit association dissociation deoxy-Hb HbCO can be followed through spectral changes which arise from these in ionization above 10.0. The difference spectrum reaction contains a contribution tryptophan. Ultracentrifuge results confirm that tetramerdimer equilibrium exists high values. tetramer-dimer constant, K4,2, increases dramatically 10.0 value K4,2 for is significantly greater than range 7 11. groups responsible change on have been tentatively identified with Tyr C7(42)α Trp C3(37)β, lie α1-β2 interface. Substantial quantities dimers are produced pH. properties examined 7.0 after rapid drop stopped flow apparatus. Association tetramer accompanied by Soret region, has allowed us follow 7.0. Deoxy-Hb react rapidly CO rate characteristic noncooperative species (l' = 6.5 x 106 m-1 sec-1). Further, haptoglobin 1-1 binds similar observed (6.3 105 sec-1 5.5 sec-1, respectively). We conclude dimer, unliganded dimer derived liganded hemoglobin, identical conformation, α1β1; first two ligand-binding properties. hemoglobin therefore minimum unit capable full cooperativity ligand binding. Models free assumed possess basically same functional as untenable.