Model for Oxygen binding to myoglobin, single site first order binding.
Binding of a ligand is a function of the affinity of the site for the ligand. The disociation constant is ratio of the off-rate, k_1, to the on-rate, k1, is Kd = k_1/k1. The binding of oxygen (O2) to myoglobin (Mb) is given by the reaction: k1 ---> O2 + Mb <--- MbO2 , where one O2 molecule binds to the site on Mb. k_1 To translate from physiological measurement of the partial pressure of O2 in units of mmHg to molar concentration, the solubility of O2 in water for the particular temperature has to be used (alphO2). The PO2 at 50% saturation, i.e. 50% of Mb bound to O2, is called p50Mb, and is the PO2 at which the molar concentration of O2 equals Kd. In this model, the PO2 is raised gradually in order to run it through a wide range of concentrations from well below Kd to well above Kd. If the rate of binding is slow, the binding will not be at equilibrium, and saturation will be below the equilibrium level when PO2 is rising fast. Change the "rateO2" at which the pO2 is raised: at low on-rates (k1) the SMb (the myoglobin saturation) will lag behind the curve for instantaneous equilibration, SMbeq. SMbeq = 1/(1+ Kd / pO2), where Kd is the dissociation constant.
The equations for this model may be viewed by running the JSim model applet and clicking on the Source tab at the bottom left of JSim's Run Time graphical user interface. The equations are written in JSim's Mathematical Modeling Language (MML). See the Introduction to MML and the MML Reference Manual. Additional documentation for MML can be found by using the search option at the Physiome home page.
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Schenkman KA, Marble DR, Burns DH, and Feigl EO: Myoglobin oxygen dissociation by multiwavelength spectroscopy. J Appl Physiol 82: 86-92, 1997. Schenkman KA, Beard DA, Ciesielski WA, and Feigl EO: Comparison of buffer and red blood cell perfusion of guinea pig heart oxygenation. Am J Physiol Heart Circ Physiol 285: H1819-H1825, 2003. Schenkman KA: Cardiac performance as a function of intracellular oxygen tension in buffer-perfused hearts. Am J Physiol Heart Circ Physiol 281: H2463-H2472, 2001.
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