The Lifetimes of Proteins Differ

The level of a protein within a cell is determined by the balance between its rates of synthesis and degradation. As a consequence, changes in protein levels can be brought about by changes either in synthetic or degradative rates. Moreover, a rapid rate of degradation ensures that the concentration of a protein rises or falls rapidly when its synthetic rate changes. 

Half-Lives of Some Proteins in Mammalian Cells 

Correlation between Half-Lives of Cytosolic Proteins and Amino Acid Residue at the N Terminal 

Methionine Glycine Alanine Serine Threonine Valine 

A second structural feature that has been correlated with protein degradative rates is the N-terminal residue of the mature form of cytoplasmic proteins. This relationship, summarized in table 29.7, has become known as the N-terminal rule. Here the presumption is that the amino-terminal residue is at least partly responsible for recognition by the degradative machinery. Proteins that are degraded according to the N-terminal rule are believed to be recognized by the ubiquitin-ATP-dependent pathway, which we describe shortly. 

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The Lifetimes of Proteins Differ Abnormal Proteins Are Selectively Degraded Proteolytic Hydrolysis Occurs in Mammalian Lysosomes... 

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