Fast time-resolved i.r. spectroscopy of biological molecules in aqueous solution: The reaction kinetics of myoglobin with carbon monoxide

Time-resolved flow-flash FT-IR difference spectroscopy: the kinetics of CO photodissociation from myoglobin revisited

“…The plot of 1/[Mb] vs. t yields a linear relationship, if the reaction follows a second-order rate law. In agreement with Dixon et al [ 25 ], the first part of the reaction ( t < 1 ms) exhibits second-order kinetics that depend on the concentrations of both the unbound myoglobin and the free carbon monoxide (Fig. 5a ).…”

“…The difference band at 1,943 cm −1 corresponds to the A 1 -band of the CO-stretching vibration. A shoulder corresponding to the A 0 -band is expected at 1,963 cm −1 , but this band is difficult to be distinguished from noise [ 6 , 25 ]. The time trace of the absorption at 1,943 cm −1 is plotted in Fig.…”

“…The time trace is fitted using the sum of two exponentials (solid trace) which yields phenomenological time constants of 185 μs and 1 ms, respectively. A detailed kinetic analysis revealed that the reaction of the deoxy state of myoglobin to carbonmonoxymyoglobin obeys (pseudo-) first-order kinetics, if the concentration of carbon monoxide does not change significantly during reaction [ 25 ]. Thus, the kinetics of the reaction are described by simple integration of the differential rate law of a first-order reaction which results in: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \ln \left[ {\text{Mb}} \right]\, = \, - k_1 \, \times \,t\,+\,c $$\end{document} were [Mb] is the concentration of the decaying deoxy state of myoglobin, k 1 the first-order rate constant, t the reaction time and c a constant that depends on the initial concentration.…”

Protein response to photodissociation of carbon monoxide from carbon monoxymyoglobin probed by time-resolved infrared spectroscopy of the amide I band

“…CO ligation is generally preferred in time-resolved spectroscopic studies due to the stability of MbCO in solution and because CO exhibits almost unit quantum efficiency for photodissociation and little geminate recombination (Gibson et al, 1986;Henry et al, 1983). Photolysis of CO from Mb and its recombination processes have been studied by a large array of spectroscopic techniques, including UV-vis absorption (Ansari et al, 1992;Henry et al, 1983;Martin et al, 1983), EXAFS (Powers et al, 1987), time-resolved circular dichroism (Xie & Simon, 1991), time-resolved infrared (TRIR) (Dixon et al, 1988;Gerwert et al, 1985;Jedju et al, 1988), and time-resolved resonance Raman (Findsen et al, 1985). These studies have focused on the ligand or the heme; information on the protein itself is indirectly inferred from these measurements.…”

“…TRIR spectroscopy has already played a large role in investigating the ligand-binding dynamics in Mb and Hb from the subpicosecond (Anfinrud et al, 1989;Jedju et al, 1988) to the millisecond time scale (Dixon et al, 1988;Gerwert et al, 1985). These studies probed the Fe-CO bleach at 1943 cm-1 and in some cases, the 2135 cm-1 (Mb) or 2100 cm-1 (Hb) absorption of photolyzed CO trapped in the heme pocket.…”