Measurement of Biotin

For measuring biotin at physiological concentrations (i.e., 100pmoll~1 to 100nmoll~1), a variety of assays have been proposed, and a limited number have been used to study biotin nutritional status. Most published studies of biotin nutritional status have used one of two basic types of biotin assays: bioassays (most studies) or avidin-binding assays (several recent studies).

Bioassays are generally sensitive enough to measure biotin in blood and urine. However, the bacterial bioassays (and perhaps the eukaryotic bioassays as well) suffer interference from unrelated substances and variable growth response to biotin analogues. Bioassays give conflicting results if biotin is bound to protein.

Avidin-binding assays generally measure the ability of biotin (i) to compete with radiolabeled biotin for binding to avidin (isotope dilution assays), (ii) to bind to avidin coupled to a reporter and thus prevent the avidin from binding to a biotin linked to solid phase, or (iii) to prevent inhibition of a bioti-nylated enzyme by avidin. Avidin-binding assays generally detect all avidin-binding substances, although the relative detectabilities of biotin and analogues vary between analogues and between assays, depending on how the assay is conducted. Chromatographic separation of biotin analogues with subsequent avidin-binding assay of the chroma-tographic fractions appears to be both sensitive and chemically specific.

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