Abstract
Vitamin B_<12> (B_<12>) is the largest and most complex compound among all vitamins, and synthesized only in certain bacteria. B_<12> is concentrated mainly in the bodies of higher predatory organisms in the natural food chain system. As animal foods, but not plant foods, are considered to be the major dietary sources of B_<12>, strict vegetarians and/or elderly persons have a great risk of developing B_<12>-deficiency. When corrinoid compounds were purified and characterized from various B_<12>-rich foods, inactive corrinoid compounds including pseudovitamin B_<12> predominated in certain shellfish and edible cyanobacteria. Significant losses of B_<12> occur in various foods during cooking and preservation. The underlying cause(s) for the link between B_<12>-deficiency and its symptoms (developmental disorder, metabolic abnormalities, and neuropathy) are poorly understood. The molecular mechanisms of these metabolic disorders were investigated using B_<12>-deficient animal models, and physiological functions of B_<12> and/or pseudo-B_<12> were also evaluated using many prokaryotic and eukaryotic organisms.
