title: Biotin-binding protein from chicken egg yolk. Assay and relationship to egg-white avidin.
abstract: 1. Biotin in chicken egg yolk is non-covalently bound to a specific protein that comprises 0.03% of the total yolk protein (0.8 mg/yolk). This biotin-binding protein is not detectable by the normal avidin assay owing to the biotin being tightly bound. Exchange of [14C]biotin for bound biotin at 65 degrees C is the basis of an assay for this protein. 2. Biotin-binding protein from egg yolk is distinguishable from egg-white avidin on Sephadex G-100 gel filtration, although the sizes of the two proteins appear quite similar. 3. Biotin-binding protein is denatured at a lower temperature and freely exchanges biotin at lower temperatures than does avidin. 4. The biotin-binding protein in egg yolk is postulated to be responsible for the deposition of biotin in egg yolk. D-[carboxyl-14C]Biotin injected into laying hens rapidly appears in the egg bound to yolk biotin-binding protein and avidin. Over 60% of the radioactivity is eventually deposited in eggs. The kinetics of biotin deposition in the egg suggests a 25 day half-life for an intracellular biotinyl-coenzyme pool in the laying hen.
mesh_terms: D000818:Animals; D001360:Avidin; D001710:Biotin / Q000378:metabolism*; D002352:Carrier Proteins; D002645:Chickens; D004527:Egg Proteins / Q000032:analysis*; D004530:Egg Yolk / Q000737:chemistry*; D005260:Female; D007700:Kinetics
chemical_list: D002352:Carrier Proteins; D004527:Egg Proteins; D001360:Avidin; D001710:Biotin