Vitamin B
12 (B
12 ) is synthesized only in certain bacteria. B
12 is concentrated mainly in the body of the higher predatory organisms in the natural food chain. Animal-derived foods such as meats, shellfish, egg, and milk are good dietary B
12 sources. In addition, a B
12 compound was contained abundantly in edible cyanobacteria. The B
12 compound present in edible cyanobacteria has been identified as pseudovitamin B
12 , an inactive corrinoid compound for humans. Therefore, this study was attempted to clarify the physiological function of pseudovitamin B
12 in cyanobacteria. The full-length of
Spirulina B
12 -dependent methionine synthase was cloned into
E.coli to clarify the physiological function of pseudovitamin B
12 in cyanobacteria. The recombinant
Spirulina enzyme showed a higher affinity for methylpseudovitamin B
12 than methylcobalamin as a cofactor, indicating that cyanobacateria can utilize pseudovitamin B
12 as the cofactor for B
12 -dependent methionine synthase.
It was further examined whether pseudovitamin B
12 exists in dietary sources other than edible cyanobacteria. As a result, a large amount of pseudovitamin B
12 was detected in turban shell and abalone, herbivorous sea snails. The content of B
12 in seaweeds which herbivorous sea snails consume as the food was very low, suggesting that pseudovitamin B
12 detected in herbivorous sea snails might be derived from cyanobacteria adhering to seaweeds.
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