van Eldik R, Zahl A (2001)
Publication Type: Journal article
Publication year: 2001
Publisher: American Chemical Society
Pages Range: 9780
Journal Issue: 123
The reduced form of aquacobalamin binds nitric oxide very effectively to yield a nitrosyl adduct, Cbl(II)-NO. UV-vis, 1H-, 31P-, and 15N NMR data suggest that the reaction product under physiological conditions is a six-coordinate, "base-on" form of the vitamin with a weakly bound α-dimethylbenzimidazole base and a bent nitrosyl coordinated to cobalt at the β-site of the corrin ring. The nitrosyl adduct can formally be described as Cbl(III)-NO-. The kinetics of the binding and dissociation reactions was investigated by laser flash photolysis and stopped-flow techniques, respectively. The activation parameters, ΔH‡, ΔS‡, and ΔV‡, for the forward and reverse reactions were estimated from the effect of temperature and pressure on the kinetics of these reactions. For the "on" reaction of Cbl(II) with NO, the small positive ΔS‡ and ΔV‡ values suggest the operation of a dissociative interchange (Id) substitution mechanism at the Co(II) center. Detailed laser flash photolysis and 17O NMR studies provide evidence for the formation of water-bound intermediates in the laser flash experiments and strongly support the proposed Id mechanism. The kinetics of the "off" reaction was studied using an NO-trapping technique. The respective activation parameters are also consistent with a dissociative interchange mechanism.
APA:
van Eldik, R., & Zahl, A. (2001). Kinetics and mechanism of the reversible binding of nitric oxide to reduced cobalamin B_12r_. Journal of the American Chemical Society, 123, 9780.
MLA:
van Eldik, Rudi, and Achim Zahl. "Kinetics and mechanism of the reversible binding of nitric oxide to reduced cobalamin B_12r_." Journal of the American Chemical Society 123 (2001): 9780.
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