Avidin
Avidin is a protein present in hen egg white and tissues of birds. In hens, it is synthesized in the oviduct and then deposited in the albumin where it protects chicken embryos from disease-causing organisms that require Biotin (vitamin H) to grow.
It is a basic tetrameric glycoprotein with four identical subunits having a combined molecular weight of 67 kDa.2 – 64 kDa.3 if calculated from aminoacid composition – and an isoelectric point of approx 10.51. The monomer Avidin contains 128 aminoacid residues.
Avidin is a remarkably stable protein. Its heat denaturation gives a transition temperature of 85°C. It is highly soluble in water and salt solutions but it crystallizes in an ammonium sulphate 3 M at a pH of approx 5. Since one tryptophan per unit is involved in the binding site, Avidin is inactivated by oxidizing agents like ozone, periodate, H2O2 or strong light.
Avidin has been suggested to act as an antibacterial protein like other egg white proteins, such as Lysozyme and Conalbumin. While its action is not yet fully ascertained it seems that its high affinity for Biotin deprives the medium of this essential growth factor. What makes Avidin significant is its high affinity for Biotin. One molecule of Avidin binds four molecules of Biotin. The Avidin-Biotin interaction is the strongest non covalent biological interaction ( Kd = 10-15 M ) between protein and a ligand. The bond formation between Biotin and Avidin is very rapid and, once formed, is unaffected by wide extremes of pH, temperature, organic solvents and other denaturing agents. The Avidin-Biotin complex is also resistant to enzymatic proteolysis.
This characteristic has favoured the Avidin usage in the following fields:
A Immunoassay
B Histochemestry
C Cytochemistry
D Biotin purification
E Chromosome visualization
Besides its use in diagnostics, Avidin is now used in the pharmaceutical field as an API. Fordras S.A. has been a forerunner in developing the use of Avidin as a marker in the treatment of tumors. This revolutionary radioimmunology technique “which has showed virtually no toxicity, has successfully been applied to the treatment of a brain tumor called gliobastoma”.
http://www.ieo.it/inglese/innovazioni/av_biot.shtml
Fordras’ Avidin is extracted from fully traceable albumin and further purified at our laboratories at Taverne near Lugano, Switzerland, where we operate according to cGMP. Besides its use in diagnostic, Avidin is now used in the pharmaceutical field as an API. Available are both lyophilized powder and solution form.
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1Green, N.M., Konieczny, L., Toms, E.J. and Valentine, R.C.: “Use of Bifunctional Biotinyl Compounds to Determine the Arrangement of Subunits in Avidin”. Biochem. J, 125 (3), 781-791, 1971.
2De Lange R.J.: “Egg White Avidin – Amino Acid Composition of the Amino- and Carboxyl- Terminal Cyanogen Bromide Peptides”. J. Biol. Chem., 245, 907-916, 1970.
3Melamed, M.D., Green, N.M.: “Avidin. 2. Purification and composition”. Biochem. J, 89, 591-599, 1963.