title: Biotin radioligand assay with an 125I-labeled biotin derivative, avidin, and avidin double-antibody reagents.
abstract: We describe a new radioligand assay for determining biotin in biological fluids by using a mixture of N-[beta-(4-OH-3-125I-phenyl)ethyl]- and N-[beta-(4-OH-3,5-di-125I-phenyl)ethyl]biotinamides as radiotracer, avidin as a binding protein, and an avidin double-antibody as a separation reagent. The radiotracer is synthesized by coupling (at pH 8.5, 20-22 degrees C, 90 min) N-hydroxysuccinimidobiotin to radioiodinated tyramine. The assay curve is linear and the assay itself is sensitive (less than 10 ng/L), reproducible (intra- and interassay CVs 4.1% and 7.0%, respectively), and allows the simultaneous handling of more than 100 samples in less than 4 h. Serum samples from apparently normal subjects contained 100-840 ng of biotin per liter (mean 340 ng/L). Pregnant women had low concentrations of biotin (100-300 ng/L) in their serum. Patients undergoing chronic hemodialysis treatment showed high concentrations (0.5-3.0 micrograms/L), which may be ascribable to the inability of avidin, which was used as the assay binding protein, to distinguish biotin from biotinyl derivatives with an intact ureido ring.
mesh_terms: D000906:Antibodies; D000888:Antibodies, Anti-Idiotypic; D001360:Avidin / Q000276:immunology; D001710:Biotin / Q000031:analogs & derivatives* / Q000097:blood; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D007553:Isotope Labeling; D007674:Kidney Diseases / Q000097:blood; D008297:Male; D011247:Pregnancy; D011786:Quality Control; D011869:Radioligand Assay; D012016:Reference Values; D006435:Renal Dialysis
chemical_list: D000906:Antibodies; D000888:Antibodies, Anti-Idiotypic; D007457:Iodine Radioisotopes; D001360:Avidin; D001710:Biotin