The relationships between the equilibrium thermodynamic properties of dissolved gas-protein interactions and the observed protein functional responses can provide valuable insights into the nature of the protein structural perturbation that underlies the response and thereby allow the pertinence of various features of hypothetical molecular mechanisms for general anesthesia to be critically evaluated. The thermodynamic properties of N2 binding to human deoxyhemoglobin (Hb) will be characterized at 37 C under high pressure conditions where the affinity of the Hb for 02 is known to be significantly increased in the presence of N2 and decreased under the influence of high hydrostatic pressure alone. The characterizations will proceed through the analysis of N2-Hb binding isotherms devived from measured N2 solubilities in buffered aqueous suspensions of intact erythrocytes and homogeneous Hb solutions at pressures up to 400 ATM. The required solubility data will be obtained in each of two experimental series using an analytic method developed by this author that allows high pressure gas solubilities in liquids to be accurately measured with only small liquid sample volumes. In one series that will include an examination of the effects of Hb-O2 saturation on Hb-N2 binding, the dissolved N2 concentration and hydrostatic pressure will be varied concurrently. In the other series, these parameters will be varied independently. Derived thermodynamic properties will be correlated with the known effects of high pressure N2 on Hb-O2 saturation kinetics in order to examine the relationships between various factors including dissolved N2 concentration, N2 binding site occupancy, N2-induced Hb conformation changes and effects on Hb-O2 affinity. In this fashion, the essential features of the molecular mechanism for high pressure N2 effects on Hb-O2 affinity will be established and compared to other mechanisms proposed for the effects of anesthetic agents on protein structure and function. Results will indicate whether the effects of high pressure N2 on Hb-O2 affinity manifest by a mechanism similar to those thought to underlie the effects of clinical anesthetics on certain Hb structural properties and will bear directly on the choice of agents used to antagonize the high pressure neurological syndrome in deep-diving man.
|Gerth, W A (1988) Nitrogen binding to deoxyhemoglobin at high pressures and its relation to changes in hemoglobin-oxygen affinity. J Biol Chem 263:13515-21|