Avidin, biotin binding affinity assay

Isotope Dilution Assay. An isotope dilution assay for biotin, based on the high affinity of avidin for the ureido group of biotin, compares the binding of radioactive biotin and nonradio active biotin with avidin. This method is sensitive to a level of 1—10 ng biotin (82—84), and the radiotracers typically used are p C]biotin (83), [3H]biotin (84,85) or an I-labeled biotin derivative (86). A variation of this approach uses I-labeled avidin (87) for the assay. 

Bioaffinity Sensing Based on the Avidin-Biotin System. Avidin is another biotin-binding protein that has been widely used in assays. Its affinity for biotin (Aatf = 1.7 X 10 M" ) is even higher than that of streptavidin (Katr = 2.5 x 10 M" ). To determine whether streptavidin or avidin is the better protein to use in PLL-g-PEG/PEGbiotin-based immunoassays, the experiments described in section 3.2 were repeated with avidin taking the place of streptavidin. 

Biotin was originally discovered as part of the complex called bios, which promoted the growth of yeast, and separately, as vitamin H, the protective or curative factor in egg white injury - the disease caused by diets containing large amounts of uncooked egg white. The glycoprotein avidin in egg white binds biotin with high affinity. This has been exploited to provide a variety of extremely sensitive assay systems. 

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