链霉亲和素是与亲和素有相似生物学特性的一种蛋白质。 链霉亲和素是streptomyces avidinii菌的分泌物，其分子量及结台生物素的能力与鸡蛋清中的亲和素相似，等电点6.0，非特异性结合远比亲和素低。

亲和素存在于鸡蛋清中，主要通过离子交换和分子筛方法提纯，从1L蛋清中可提取纯AV15~25mg。

链霉亲和素是Streptomyces avicllrdi菌培养过程中的分泌产物，主要通过2一亚氨基生物索亲和层析法提纯，1L培养液中含蛋白1 0~60mg 。 

一条完整的链霉亲和素肽链中有159个氨基酸残基，分子量为16450，而亲和素 的一条肽链其含128个氨基酸残基，但分子量也达15600，两者十分接近，这是因为链霉亲和素 的氨基酸中，甘、丙氨基酸含量较大，且又不含任何糖基，而亲和素的每条肽链含4个甘露糖，3个氨基葡糖，含糖量达lO ，故分子量相对较大。

消光系数与蛋白中Tyr含量有关， 由于链霉亲和素中Tyr的含量比亲和素 多，所以链霉亲和素的比消光系数也较亲和素为高，两者分别为E 1mg/ml=3．40和E1mg/ml=1.57。

在282nm 上这两种蛋白结合生物素后并不改变其消光系数，而在233nm上，它们结合生物素后郡便其消光系数值增高，现在一般都是利用蛋白的这种吸光特点来测定它们的活性。

Streptavidin is a protein with similar biological characteristics to avidin. Streptavidin is the secretion of Streptomyces avidinii. Its molecular weight and the ability of Jietai biotin are similar to those in egg white. Its isoelectric point is 6.0, and its nonspecific binding is much lower than that of avidin.

Avidin exists in egg white and is mainly purified by ion exchange and molecular sieve. Pure av15 ~ 25mg can be extracted from 1L egg white.

Streptavidin is the secretory product of Streptomyces avichlrdi during the culture process. It is mainly purified by 2-imino biological cord affinity chromatography. The protein in 1L culture medium is 10 ~ 60mg.

A complete streptavidin peptide chain has 159 amino acid residues with a molecular weight of 16450, while a peptide chain of streptavidin contains 128 amino acid residues with a molecular weight of 15600, which is very close to each other. This is because the amino acids of streptavidin contain large amounts of glycine and propylene amino acids without any sugar groups, while each peptide chain of streptavidin contains 4 mannose and 3 glucosamine with a sugar content of lo, Therefore, the molecular weight is relatively large.

The extinction coefficient is related to the Tyr content in protein. Because the Tyr content in streptavidin is more than that in avidin, the specific extinction coefficient of streptavidin is also higher than that of avidin, e 1mg / ml = 3.40 and e 1mg / ml = 1.57 respectively.

At 282nm, these two proteins do not change their extinction coefficient after binding biotin. At 233nm, their extinction coefficient increases after binding biotin. Now, their activity is generally measured by using the light absorption characteristics of proteins.