title: Kinetic and thermodynamic parameters for oxygen binding to the allosteric states of Panulirus interruptus hemocyanin.
abstract: The temperature dependence of the oxygen binding equilibria and kinetics of Panulirus interruptus hemocyanin has been analyzed within the context of the two-state allosteric model. Oxygenation of the T-state is characterized by a more negative value of DeltaH than that of the R-state; therefore, cooperative effects in oxygen binding to P. interruptus hemocyanin are thermodynamically governed by favorable entropy changes. The allosteric transition in the unliganded derivative shows an enthalpy-entropy compensation effect. The activation enthalpies for oxygenation and deoxygenation of the T-state are larger than those for the R-state, while the activation entropies are favorable for the T-state and unfavorable for the R-state. Thus, the activation free energies for oxygen binding to the T- and R-states are similar, while for the deoxygenation reaction DeltaG++ is smaller for the T-state. The analysis reported confirms the applicability of the Monod-Wyman-Changeux two-state allosteric model to P. interruptus hemocyanin and yields a complete thermodynamic characterization of oxygen binding under both equilibrium and dynamic regimes.
authors.affiliation: Institute of Chemistry and CNR Centre for Molecular Biology, and Department of Biochemistry, Faculty of Medicine, II University of Rome, 00185 Rome, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Antonini
authors.forename: M
authors.initials: M
authors.lastname: Brunori
authors.forename: A
authors.initials: A
authors.lastname: Colosimo
authors.forename: H A
authors.initials: HA
authors.lastname: Kuiper
authors.forename: L
authors.initials: L
authors.lastname: Zolla