Homogeneous enzyme-linked competitive binding assay for biotin based on the avidin-biotin interaction

A homogeneous enzyme-linked competitive-binding assay for biotin with glucose-6-phosphate dehydrogenase (G6PDH), is described. This assay is based on the interaction between a G6PDH/biotin conjugate with avidin, a natural binder for biotin. In the absence of biotin in the assay mixture, this interaction results in 100% inhibition of the enzyme conjugate. In the presence of biotin, the enzymatic activity of the conjugate is regained in an amount related to the concentration of the vitamin in the sample. Extremely steep, gate-like dose/response curves, attributable to the relative binding affinities of avidin for biotin and the conjugate, are observed. The detection limits of the system vary with the amounts of avidin and enzyme/biotin conjugate used. The method is rapid and sensitive and is evaluated for the direct determination of biotin in vitamin tablets.