Sandbox 32: Difference between revisions

Trypsin is a medium size globular protein that functions as a pancreatic serine protease. This enzyme hydrolyzes bonds by cleaving peptides on the C-terminal side of the amino acid residues lysine and arginine. It has also been shown that cleavage will not occur if there is a proline residue on the carboxyl side of the cleavage site. Trypsin was first discovered in 1876 by Kuhne, who investigated the proteolytic activity of the enzyme. In 1931 the enzyme was purified by crystallization by Norothrop and Kunitz and later in 1974 the three dimensional structure of trypsin was determined. Throughout the 1990's the role of trypsin in hereditary pancreatitis and the mutation that causes it was discovered.  Today trypsin is used in the development of cell and tissue protocols, as well as in the medical field to determine the role of trypsin in pancreatic diseases<ref>Trypsin. 2010. 30 October 2010 <http://www.worthington-biochem.com/tyr/default.html></ref>.

Trypsinogen is the precursor form or zymogen of Trypsin. Zymogens are enzyme precursors that are made and secreted in the lysosome of the cell. Zymogens are not active until they go through a chemical process such as hydrolysis, cleavage, or other cleavages that reveal the active site. The zymogen precursor is necessary in order to prevent the destruction of cellular proteins and to allow the enzyme to be in it's active state only when in appropriate conditions. Trypsinogen is specifically produced in the exocrine cells of the pancreas. There are three isoforms of Trypsinogen that are secreted by the pancreas. The precursor is only activated when it reaches the lumen of the small intestine. This activation occurs through the help of an enteropeptidase and once activated trypsin stimulates the formation of more trypsinogen<ref>Trypsin. 30 October 2010 <http://www.sigmaaldrich.com/life-science/metabolomics/enzyme-explorer/analytical-enzyme/trypsin.html>.</ref>. The structure of Bovine Trypsinogen is shown in the figure to the right <ref> Image From: http://chemistry.umeche.maine.edu/MAT500/Peptidase1.html</ref>.  

=Catalytic Mechanism=

The function of Trypsin is to break down peptides using a hydrolysis reaction into amino acid building blocks. This mechanism is a general catalytic mechanism that all Serine proteases use.  The active site where this mechanism occurs in Trypsin is composed of three amino acids and called a <scene name='Sandbox_45/Ctriadd102h57s195/4'>catalytic triad</scene>. The three catalytic residues are Serine 195, Histidine 57, and Aspartate 102 <ref>Pratt, C.W., Voet, D., Voet, J.G. Fundamentals of Biochemistry - Life at the Molecular Level - Third Edition. Voet, Voet and Pratt, 2008.</ref>. The structure of the catalytic triad and the mechanism are shown in the figures to the right. In the mechanism, serine is bonded to the imidazole ring of the histidine. When histidine accepts a proton from serine an alkoxide nucleophile is formed. This nucleophile attacks the substrate when the substrate is present. The role of the aspartate residue is hold histidine in the proper position to make it a good proton acceptor. What makes this mechanism works is that a pocket if formed from the three residues and the three residues function to hold each other in proper position for nucleophilic attack.  

The steps of the mechanism involve two tetrahedral intermediates and an Acyl-enzyme intermediate <ref>Structural Biochemistry. 10 June 2010. 30 October 2010.<http://en.wikibooks.org/wiki/Structural_Biochemistry/Enzyme/Catalytic_Triad>.</ref>. The mechanism can be followed in more detail in the figure on the right <ref>Image From: http://www.bmolchem.wisc.edu/courses/spring503/503-sec1/DRAWINGS/503-3a-2serineprotease.jpg</ref>.