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  • Title: Investigation on binding of nitric oxide to horseradish peroxidase by absorption spectrometry.
    Author: Qiang L, Zhu S, Ma H, Zhou J.
    Journal: Spectrochim Acta A Mol Biomol Spectrosc; 2010 Jan; 75(1):417-21. PubMed ID: 19944641.
    Abstract:
    Binding of nitric oxide to horseradish peroxidase (HRP) has been investigated by absorption spectrometry in 0.2M anaerobic phosphate buffer solution (pH 7.4). Based on this binding equilibrium, a model equation for evaluating the binding constant of nitric oxide to HRP is developed and the binding constant is calculated to be (1.55+/-0.06)x10(4)M(-1), indicating that HRP can form a stable complex with nitric oxide. The type of inhibition by nitric oxide is validated on the basis of studying initial reaction rates of HRP-catalyzed oxidation of guaiacol in the presence of hydrogen peroxide and nitric oxide. The inhibition mechanism is found to follow an apparent non-competitive inhibition by Lineweaver-Burk method. Based on this kinetic mechanism, the binding constant is also calculated to be (5.22+/-0.06)x10(4)M(-1). The values of the binding constant determined by the two methods are almost identical. The non-competitive inhibition model is also applicable to studying the effect of nitric oxide on other metalloenzymes, which catalyze the two-substrate reaction with the "ping-pong" mechanism.
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