Temperature dependent quaternary state relaxation in sol-gel encapsulated hemoglobin

Samples of human adult hemoglobin (HbA) encapsulated in a wet porous sol-ge l are prepared under aerobic and anaerobic conditions. Resonance Raman spec troscopy is used to compare equilibrium deoxyHbA to the nonequilibrium deox y species generated by deoxygenating an encapsulated oxyHbA sample. The spe ctra of the deoxygenated samples as a function of delay subsequent to deoxy genation reveal a marked slow down by the gel of the two phases of relaxati on: the tertiary relaxation associated with the transition from the ligande d R to deoxy R conformations and the quaternary relaxation associated with the deoxy R to deoxy T transition. The temperature dependence (4-80 degrees C) of the relaxation indicates that the internal viscosity of the gel is g reatly enhanced at the lower temperatures. At 80 degrees C the tertiary and quaternary relaxations occur over minutes to hours, respectively, whereas at 4 degrees C both relaxations are essentially frozen. These results demon strate the impressive potential of using sol-gel encapsulation as a means o f studying substrate binding induced conformational changes in proteins. (C ) 1999 John Wiley & Sons, Inc.