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. 2001 Apr 1;355(Pt 1):131–137. doi: 10.1042/0264-6021:3550131

Protein-coenzyme interactions in adenosylcobalamin-dependent glutamate mutase.

M S Huhta 1, H P Chen 1, C Hemann 1, C R Hille 1, E N Marsh 1
PMCID: PMC1221720  PMID: 11256957

Abstract

Glutamate mutase catalyses an unusual isomerization involving free-radical intermediates that are generated by homolysis of the cobalt-carbon bond of the coenzyme adenosylcobalamin (coenzyme B(12)). A variety of techniques have been used to examine the interaction between the protein and adenosylcobalamin, and between the protein and the products of coenzyme homolysis, cob(II)alamin and 5'-deoxyadenosine. These include equilibrium gel filtration, isothermal titration calorimetry, and resonance Raman, UV-visible and EPR spectroscopies. The thermodynamics of adenosylcobalamin binding to the protein have been examined and appear to be entirely entropy-driven, with DeltaS=109 J.mol(-1).K(-1). The cobalt-carbon bond stretching frequency is unchanged upon coenzyme binding to the protein, arguing against a ground-state destabilization of the cobalt-carbon bond of adenosylcobalamin by the protein. However, reconstitution of the enzyme with cob(II)alamin and 5'-deoxyadenosine, the two stable intermediates formed subsequent to homolysis, results in the blue-shifting of two of the bands comprising the UV-visible spectrum of the corrin ring. The most plausible interpretation of this result is that an interaction between the protein, 5'-deoxyadenosine and cob(II)alamin introduces a distortion into the ring corrin that perturbs its electronic properties.

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Selected References

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