NeutrAvidin, Avidin, Streptavidin的区别
Avidin(亲和素)：是一种醣蛋白，被发现存在于鸡蛋卵白中，所以中文称之为「卵白素」，在鸟类、爬虫类及两栖类的组织中亦存在。Avidin 总分子量为 67,000 Daltons，由四个完全相同的次体 (subunit)所组成，每个次体皆能与一分子的 biotin 结合。Avidin 含醣比例颇高，约占了总分子量的 10％。其 pI＝10-10.5，溶于水及含盐溶液中。Avidin 在相当广的温度及 pH 范围下皆很稳定。
NeutrAvidin: 是去除了”醣”以后的 Avidin，分子量为 60,000 daltons。其优点为 pI 值为中性，且其与biotin-binding protein 之间会造成的非专一性结合为最低。
Streptavidin(链霉亲和素): 由 Steptomyces Avidinii 中纯化出的蛋白质，同样能与 Biotin 做专一性结合，分子量为 60,000 daltons。Streptavidin 也是个由四个相同次体 (subunit)所组成的蛋白质，每个次体皆能与一分子的 biotin 结合，且其与 biotin 之键结亲和力相当于 Avidin-biotin 之亲和力。不过Biotin-Streptavidin 复合物对于 guanidine.HCl 将两者分开的抗拒能力较 Biotin-Avidin 还要强。此外，Streptavidin 不含醣且具有酸性的 pI = 5，正好与Avidin 相反。
1. Near-neutral isoelectric point—pI = 6.3, more neutral than native avidin
2. Nearly devoid of glycosylation—decreased possibility of lectin binding compared to native avidin
3. No RYD recognition sequence—no known off-target binding domains like streptavidin
4. Affordable—significantly less expensive than streptavidin
NeutrAvidin Protein is deglycosylated native avidin from egg whites. Removal of the excess carbohydrate by an exclusive process yields a protein with a more neutral isoelectric point and less nonspecific binding properties. Purified NeutrAvidin Protein provides exceptional performance in western blot, ELISA, and IHC applications that require biotin-binding probes. Assay specificity, sensitivity, and signal-to-noise ratios with NeutrAvidin Protein are generally equivalent or better than with the significantly more expensive streptavidin.
Avidin is a glycoprotein found in the egg white and tissues of birds, reptiles, and amphibia. The biotin-binding protein contains four identical subunits having a combined mass of 67,000-68,000 daltons. Removing the glycosylation from avidin yields NeutrAvidin Protein with a mass of 60,000 daltons. Carbohydrate-based lectin binding is reduced to undetectable levels, yet biotin-binding affinity is retained. NeutrAvidin Protein offers the advantages of a neutral pI to minimize nonspecific adsorption, along with lysine residues that remain available for derivatization or other customized conjugation. NeutrAvidin Protein yields the lowest nonspecific binding among the known biotin-binding proteins. The specific activity for biotin binding is approximately 14 µg/mg of protein, which is near the theoretical maximum activity.
Streptavidin is a bacterially derived biotin-binding protein that reportedly exhibits less nonspecific binding than avidin
Capacity: Binding activity of streptavidin is determined to be >11 units per mg protein. One unit of binding activity is defined as that amount of protein which binds 1 µg of biotin (Green, N.M., Biochem. J., 89:599,1963)