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Updated: Oct 3, 2026

Sequence-specific Labeling of Nucleic Acids and Proteins with Methyltransferases and Cofactor Analogues
Published on: November 22, 2014
Evidence for the Unexpected Associative Displacement of Adenosyl by Cyanide in Coenzyme B(12)
Nicola E. Brasch1, Mohamed S. A. Hamza, Rudi van Eldik
1Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany.
Abstract:
The reaction of coenzyme B(12) (adenosylcobalamin) with cyanide has been reinvestigated in detail using spectroscopic and kinetic techniques. It has been shown that this reaction proceeds in one kinetically observable step, contradicting previous findings, with rate-determining attack of the first cyanide (k = (7.4 +/- 0.1) x 10(-3) M(-1) s(-1), 25.0 degrees C, I = 1.0 M (NaClO(4))). The activation parameters were found to be DeltaH() = 53.0 +/- 0.6 kJ mol(-1), DeltaS() = -127 +/- 3 J mol(-1) K(-1) and DeltaV() = -10.0 +/- 0.4 cm(3) mol(-1), suggesting an associative displacement mechanism. It is postulated that attack of the first cyanide occurs at the beta-(5'-deoxy-5'-adenosyl) site rather than at the alpha-dimethylbenzimidazole site.
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