抄録
Vitamin B_<12> compounds have been intriguing subjects of investigation for inorganic and organometallic chemists for a long time, because vitamin B_<12> and its coenzyme forms are a cobalt complex and organocobalt compounds, respectively. Recently, many X-ray structures of B_<12>-dependent enzymes have become available, and the functional roles of B_<12> coenzymes in enzymatic reactions have been elucidated on the bases of their three-dimensional structures. The fine mechanisms of B_<12> catalyses in these enzymes are the main subjects of this review. In addition, some B_<12> enzymes contain metal ions other than B_<12> coenzymes and their roles are interesting. Furthermore, in some non-B_<12> but isofunctional enzymes, metal ion-containing components seem to function as a substitute for B_<12>. The biochemistry of these types of metal ions that are related to the functions of B_<12> is also included in this review.
