Photolytic Cleavage of Co–C Bond in Coenzyme B12-Dependent Glutamate Mutase

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 B12). 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 ∆S = 109 Jċmol-1ċK-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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Cloning, sequencing and expression inEscherichia coliof the gene encoding component S of the coenzyme B12-dependent glutamate mutase fromClostridium cochlearium

FEMS Microbiology Letters ◽

10.1111/j.1574-6968.1994.tb06797.x ◽

1994 ◽

Vol 118 (1-2) ◽

pp. 15-21 ◽

Cited By ~ 10

Author(s):

Oskar Zelder ◽

Birgitta Beatrix ◽

Wolfgang Buckel

Keyword(s):

Coenzyme B12 ◽

Gene Encoding ◽

Glutamate Mutase ◽

Sequencing And Expression

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Review Article Coenzyme-B12-Dependent Glutamate Mutase

Bioorganic Chemistry ◽

10.1006/bioo.2000.1168 ◽

2000 ◽

Vol 28 (3) ◽

pp. 176-189 ◽

Cited By ~ 37

Author(s):

E.Neil G. Marsh

Keyword(s):

Review Article ◽

Coenzyme B12 ◽

Glutamate Mutase

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Insights into the mechanisms of adenosylcobalamin (coenzyme B12)-dependent enzymes from rapid chemical quench experiments

Biochemical Society Transactions ◽

10.1042/bst0370336 ◽

2009 ◽

Vol 37 (2) ◽

pp. 336-342 ◽

Cited By ~ 9

Author(s):

E. Neil G. Marsh

Keyword(s):

Free Radicals ◽

Steady State ◽

Kinetic Isotope Effect ◽

Hydrogen Transfer ◽

Coenzyme B12 ◽

Hydrogen Atoms ◽

Glutamate Mutase ◽

Kinetic Isotope ◽

Steady State Kinetic ◽

State Kinetic

Glutamate mutase is one of a group of adenosylcobalamin-dependent enzymes that use free radicals to catalyse unusual and chemically difficult rearrangements involving 1,2-migrations of hydrogen atoms. A key mechanistic feature of these enzymes is the transfer of the migrating hydrogen atom between substrate, coenzyme and product. The present review summarizes recent experiments from my laboratory that have used rapid chemical quench techniques to identify intermediates in the reaction and probe the mechanism of hydrogen transfer through a variety of pre-steady-state kinetic isotope effect measurements.

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