牛血清白蛋白Bovine serum albumin （BSA） makes up approximately 60% of all proteins in animal serum.
牛血清白蛋白的基本性質
Number of residues：607
Molecular weight：69323.4 Da
pI in water at 25 ℃： 4.7
Optical absorbance of 1 g/l at 279nm： 0.667 mL mg-1 cm-1 at 279nm
Dimensions： 40x40x140 cubic angstroms
A 18-residue signal peptide is cut off from the precursor protein upon secretion, hence the precursor has 607 amino acid residues and a molecular weight of 69.4 kDa.
不同濃度單位的換算
牛血清白蛋白溶液常用的濃度單位是質量體積百分比（g/ml）如：1%、0.1%；和質量/體積比如10mg/ml。
這兩種單位的換算如下：
1% BSA = 10 mg/ml BSA；0.1% BSA = 1 mg/ml BSA
根據BSA的分子量為69 KDa可以估算出：
10 mg/ml BSA = 0.145 mM = 145 μM
牛血清白蛋白的應用
1、細胞培養時作為添加劑
It is commonly used in cell culture protocols, particularly when protein supplementation is necessary and the other components of serum are unwanted. In cell culture its main role is as a carrier of small molecules. Because of its negative charge, BSA binds water, salts, fatty acids, vitamins and hormones, then carries these bound components between tissues and cells. The binding capacity also makes BSA an effective scavenger for removing toxic substances, including pyrogens, from the medium.
2、作為其他酶的保護劑
eg. In restriction digests, BSA is used to stabilize some enzymes during digestion of DNA and to prevent adhesion of the enzyme to reaction tubes and other vessels.
3、 **組化實驗中作為封閉劑
eg. ELISAs （Enzyme-Linked Immunosorbent Assay）, immunoblots, and immunohistochemistry
4、蛋白定量時作為標準物
eg. Bradford Assay, BCA assay
5、一些酶活測定反應中作為陰性對照
eg. DNA binding assay
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