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鏈霉親和素是與親和素有相似生物學(xué)特性的一種蛋白質(zhì)。 鏈霉親和素是streptomyces avidinii菌的分泌物，其分子量及結(jié)臺(tái)生物素的能力與雞蛋清中的親和素相似，等電點(diǎn)6.0，非特異性結(jié)合遠(yuǎn)比親和素低。

親和素存在于雞蛋清中，主要通過(guò)離子交換和分子篩方法提純，從1L蛋清中可提取純AV15~25mg。

鏈霉親和素是Streptomyces avicllrdi菌培養(yǎng)過(guò)程中的分泌產(chǎn)物，主要通過(guò)2一亞氨基生物索親和層析法提純，1L培養(yǎng)液中含蛋白1 0~60mg 。 

一條完整的鏈霉親和素肽鏈中有159個(gè)氨基酸殘基，分子量為16450，而親和素 的一條肽鏈其含128個(gè)氨基酸殘基，但分子量也達(dá)15600，兩者十分接近，這是因?yàn)殒溍褂H和素 的氨基酸中，甘、丙氨基酸含量較大，且又不含任何糖基，而親和素的每條肽鏈含4個(gè)甘露糖，3個(gè)氨基葡糖，含糖量達(dá)lO ，故分子量相對(duì)較大。

消光系數(shù)與蛋白中Tyr含量有關(guān)， 由于鏈霉親和素中Tyr的含量比親和素 多，所以鏈霉親和素的比消光系數(shù)也較親和素為高，兩者分別為E 1mg/ml=3．40和E1mg/ml=1.57。

在282nm 上這兩種蛋白結(jié)合生物素后并不改變其消光系數(shù)，而在233nm上，它們結(jié)合生物素后郡便其消光系數(shù)值增高，現(xiàn)在一般都是利用蛋白的這種吸光特點(diǎn)來(lái)測(cè)定它們的活性。

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.