Infrared-monitored flash-photolysis of carboxymyoglobin

Abstract

An infrared-monitored flash-photolysis apparatus capable of measuring absorbance changes to 10\sp{-3}OD over a time range from 10$\mu$s to 10s is described. Measurements made on this apparatus, combined with slower measurements made on a Fourier-transform infrared spectrometer, of the CO-rebinding kinetics of the A\sb0, A\sb1, and A\sb3 conformations of sperm-whale myoglobin (Mb) at atmospheric pressure and neutral pH are reported. The A\sb0, A\sb1, and A\sb3 rebinding kinetics are shown to be non-exponential and parameterized by activation-enthalpy distributions differing in prefactor k\sb0\ (\log(k\sb0/s) = 10.8, 9.3, and 9.8 for the A\sb0, A\sb1, and A\sb3 conformations, respectively) and peak activation-enthalpy H\sb{p}\ (H\sb{p} = 10.4, 9.6, and 17.6 kJ/M, respectively).CO-rebinding kinetics of MbCO ensembles prepared along different paths in the pressure-temperature plane ("freeze" and "squeeze-freeze-release" ensembles) monitored at two frequencies within the A\sb1 band are also reported. No differences between kinetics monitored at 1943.0cm\sp{-1} and 1947.5cm\sp{-1}, and none between the kinetics of the freeze and squeeze-freeze-release ensembles, are resolved. The large uncertainty in the determination of the peak H\sb{p} of the activation-enthalpy distribution (H\sb{p} = 15 (+8,$-$7)kJ/M for the squeeze-freeze-release ensemble monitored at 1943.0cm\sp{-1}) suggests limits of the capability of the apparatus, which are discussed in terms of time resolution.U of I OnlyETDs are only available to UIUC Users without author permissio