Harris R J
Analytical Chemistry Department, Genentech, Inc., South San Francisco, CA 94080, USA.
J Chromatogr A. 1995 Jun 23;705(1):129-34. doi: 10.1016/0021-9673(94)01255-d.
C-terminal Lys or Arg residues whose presence was expected based on gene sequence information are often absent in proteins isolated from mammalian cell culture. This discrepancy is believed to be due to the activity of one or more basic carboxypeptidases. Internal Arg/Lys residues that become C-terminal upon proteolysis or zymogen activation, such as in the two-chain form of tissue plasminogen activator, may also be removed from the mature protein. Charge heterogeneity results when this type of processing is incomplete; such heterogeneity can be detected by isoelectric focusing or ion-exchange chromatography. The absence of C-terminal basic residues is not usually a regulatory concern, as plasma-derived proteins are often similarly processed.
基于基因序列信息预期会存在的C末端赖氨酸或精氨酸残基，在从哺乳动物细胞培养物中分离出的蛋白质中常常缺失。这种差异被认为是由于一种或多种碱性羧肽酶的活性所致。蛋白水解或酶原激活后成为C末端的内部精氨酸/赖氨酸残基，例如组织纤溶酶原激活物的双链形式中的此类残基，也可能从成熟蛋白中被去除。当这种类型的加工不完全时会导致电荷异质性；这种异质性可通过等电聚焦或离子交换色谱法检测到。C末端碱性残基的缺失通常不是一个调节方面的问题，因为血浆来源的蛋白质常常也会进行类似的加工。
