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Abstract: This review deals with results from crystallographic studies on proteins that interact with the essential micronutrient cobalamin (vitamin B12). Both B12-dependent enzymes and B12-transport proteins are described with an emphasis on structural aspects of cobalamin and its protein environment. [Copyright &y& Elsevier]

Redox potentials of a series of complexes of cobalt(II) and organocobalt(III) with tetraazamacrocyclic (N) and NO-noncyclic polychelate ligands have been determined by cyclic voltammetry. Introduction of an o-phenylene fragment instead of an ethylene fragment into an equatorial ligand and/or exchange of an N-coordination chromophore for the NO-analog has been shown to result in the anodic shift of redox potentials of MeCo(IV)L/ MeCo(III)L, MeCo(III)L/MeCo(II)L, and Co(II)L/Co(I)L pairs. It has been established that the solvent effect on redox potential is larger for Co(III)L/Co(II)L than for other pairs. Apparently, this is the first case when quasi-reversible stages of oxidation of MeCo(III)L to MeCo(IV)L and MeCo(IV)L to [MeCo(IV)L] can be simultaneously observed. A. relatively stable complex of methylcobalt(IV) with a long lifetime at ∼20 °C has been registered by the ESR method. [ABSTRACT FROM AUTHOR]