Energetics of subunit assembly and ligand binding in human hemoglobin

Journal Article · Wed Oct 01 00:00:00 EDT 1980 · Biophys. J.; (United States)

DOI:https://doi.org/10.1016/S0006-3495(80)84960-5· OSTI ID:7032644

Ackers, G K

An extensive and self-consistent set of thermodynamic properties has recently been established for the coupled processes of subunit assembly and ligand binding (oxygen and protons) in human hemoglobin. The resulting thermodynamic values permit a consideration of the possible sources of cooperative energy. The analysis indicates that: (a) the change in buried surface area upon oxygenation (i.e., hydrophobic stabilization) does not play a dominant role in stabilizing the unliganded tetramer relative to the liganded tetramer; (b) the pattern of enthalpic and entropic contributions to the free energies of dimer-tetramer assembly provides evidence against a dominant role of salt bridges in stabilizing the deoxy tetramer; (c) the thermodynamic results are consistent with a dominant role of increased hydrogen bond formation in the deoxy quaternary structure; (d) within tetramers the variation in free energy for successive oxygenation steps arises from both enthalpic and entropic contributions and the enthalpic contributions are almost entirely attributable to the heats of Bohr proton release. At pH 7.4 the patterm of thermodynamic values suggests that a large contribution to the free energy of cooperativity may arise from the energetics of Bohr proton release. It is suggested that a combination of proton ionization and hydrogen bonding may account for the main energetic features of cooperativity. Possible contributions from fluctuation behavior cannot presently be evaluated.

• Research Organization: Johns Hopkins Univ., Baltimore, MD
• OSTI ID: 7032644
• Journal Information: Biophys. J.; (United States), Vol. 32:1
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
HEMOGLOBIN
THERMODYNAMICS
LIGANDS
BIOCHEMICAL REACTION KINETICS
BIOPHYSICS
ENTHALPY
ENTROPY
FREE ENERGY
INTERMOLECULAR FORCES
MAN
MOLECULAR STRUCTURE
SURFACE AREA
ANIMALS
CARBOXYLIC ACIDS
ENERGY
GLOBIN
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
MAMMALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHYSICAL PROPERTIES
PIGMENTS
PORPHYRINS
PRIMATES
PROTEINS
REACTION KINETICS
SURFACE PROPERTIES
THERMODYNAMIC PROPERTIES
VERTEBRATES
550200* - Biochemistry
551000 - Physiological Systems