Abstract
For the purpose to examine the usefulness of the plate method for the determination of cobalamin in natural products, several animal samples were used and parallel assay was made with the turbidimetric method. In all samples their estimates of cobalamin content by the plate method were considerably lower than those determined by the turbidimetric ones. Furthermore, the recoveries of the added cyanocobalamin to these extracts were unsatisfactory and the dose-response lines from them were not parallel to that from pure cobalamin solutions. These results strongly suggest that in the extracts there are some factors interfering the valid assays of cobalamin by the plate method. As one of these factors, methionine content in the extracts was especially marked. The satisfactory assays of vitamin B_<12> in biological materials by this method can not be expected unless an improvement in extracting procedure of the vitamin from them will be detected.
