A competitive inhibition radioassay of thiamine is described using a gel obtained by coupling a buckwheat-seed thiamine-binding protein to CNBr-activated Sepharose. The sample to be analysed is incubated with gel suspension and [14C]thiamine and after centrifugation the radioactivity of the supernatant is measured. The method is simple and specific, and applicable over a thiamine concentration range 0.5-5 microM with a coefficient of variation typically below 5%. The gel is reusable and stable for several months. Applicability of the method for direct determination of thiamine in multivitamin pharmaceuticals is demonstrated.

To identify vitamin B₁₂-binding proteins in egg white, an affinity chromatographic isolation procedure was applied. A fraction tightly adsorbed on vitamin B₁₂ immobilized in agarose was eluted with 1 mM cyanocobalamin, and then separated by isoelectric focusing in sucrose density gradient. Two isolated proteins (or perhaps two forms of the same protein) of isoelectric points 6.2 and 7.2 and the same M_r 90,000 were found capable of detectable vitamin B₁₂ binding. They are probably glycoproteins, each composed of a single polypeptide chain.

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