Avidin affinity constant with biotin

Biotin has served this purpose well in both nucleic acid and antibody probe systems. As well as being easily detected with immunoglobulins specific for biotin, biotin may also be detected non-immunologically with avidin or streptavidin, two proteins which share a marked, highly specific affinity for biotin. The affinity constant for avidin-biotin interactions is approximately 10 - liters/mole, much higher than the range for antigen-antibody interactions which are commonly between 10 -10 liters/mole. Consequently, a vast number of detection complexes composed of avidin or streptavidin bound to a detection system are commercially available (e.g. streptavidin-alkaline phosphatase). 

Incorporation of other biological components such as biotin-avidin coupling has also been used. The system has an affinity constant of 10 M and is resistant to extreme pH, vigorous washings and chaotroping conditions. Generally they are used in conjunction with other immobihsation methods. 

Avidin hound complex. Avidin is a tetrameric biotin-binding protein produced in egg whites. The tetrameric protein contains four identical subunits (homotetramer), each of which can bind to biotin with a high degree of affinity and specificity. The dissociation constant of avidin is measured to be. Kid 10 M, making it one of the strongest known non-covalent bonds. 

When two molecules need to be non-covalently brought together in the creation of a device, one can exploit the natural interaction between biotin and avidin. Biotin is a cofactor that binds to the protein receptor avidin (or strep-avidin), and the binding constant has been measured to be near 10 - M h This is one of the largest affinities associated with any molecular recognition event, and can be considered irreversible. Avidin is a tetrameric protein that binds four biotins independently. The fact that the protein binds four biotins and has such a large affinity for each, makes this system a powerful tool for assembly processes. 

Antibodies form complexes with their respective antigens (here analytes). These complexes can show a particular strength, which can be quantified by the affinity constant (or equilibrium constant). This affinity constant is about 10 -10 L mol for most analytically useful antibodies. The higher this number, the more stable is the complex. The highest known affinity in the biochemical field is the interaction between avidin (an egg protein) and biotin (vitamin H), for which a value of around 10 L mol has been determined. The affinity constant plays an important role in immunoassays and other immunological techniques. The development of new methods is greatly facilitated if this constant is known. 

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