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From: Rebekah Healy
Date: 05 Feb 2004
Time: 19:36:43 -0500
Remote Name: 172.16.10.43
To answer your question, it is because proteases are specific for certain amino acids. This means that a protease will cleave only upon recognition of certain amino acids. As a matter of fact, it is with a great deal of specificity. Basically, it’s all because of the shape and composition of the active site within each individual protease. For example, a protease, Trypsin, will cleave after lys and arg residues (because trypsin interacts with the positive charge on both residues). Chymotrypsin, another protease, cleaves after aromatic and large hydrophobic residues (because the active site contains a hydrophobic pocket that these residues fit real nice in). So in other words, some amino acids just fit better than others within a protease. These come in real handy when trying to sequence proteins in the lab, but the main function for proteases in the body is the degradation of unwanted ‘stuff’ in the body – the cleavage of the peptide bond is an irreversible step. Certain proteases are also responsible for blood coagulation. So proteases are very effective in their duties (so effective that researchers are looking at proteases as new drug therapies for several conditions such as cardiovascular diseases (proteases are now used to treat heart failure and even to prevent heart attacks in at-risk patients, such as people with diabetes). I found some good websites that might give some more detail on proteases. http://www.enzymeessentials.com/HTML/proteases.html http://www.nature.com/horizon/proteases/background/prespective.htm