A radioimmunoassay for chicken avidin. Comparison with a [14C]biotin-binding method

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Abstract
A double-antibody solid-phase radioimmunoassay for chicken avidin is reported. Avidin was labeled with 125I by the chloramine-T method. The bound and free avidin were separated with a 2nd antibody bound to a solid matrix. In the logit-log scale the standard curve was linear from 1-2 to 100-200 ng of avidin/ml. Cross-reaction of ovalbumin was less than 0.015%. Saturation of biotin-binding sites of avidin with an excess of biotin decreased radioimmunoassay values by about 15%. Recovery studies indicated that avidin can be assayed from all chicken tissues studied with radioimmunoassay, whereas the [14C]biotin/bentonite method gave poor recoveries for avidin in the liver and kidney. Radioimmunoassay and the [14C]biotin/bentonite method gave similar concentrations for oviduct avidin.