ch369_sp11_enz_2_notes

ch369_sp11_enz_2_notes - uncatalyzed reaction catalyzed...

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Tetrahedral intermediate  stabilized in chymotrypsin  active site. By stabilizing the tetrahedral intermediate, chymotrypsin lowers the  activation energy for the reaction.  So instead of taking years to  cleave a peptide bond, chymotrypsin can cleave 190 peptides per  second. uncatalyzed  reaction catalyzed  reaction
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At pH 7, you would  not  expect Histidine to remove a proton from  Serine (because pKa of His is 6, pKa of serine is > 12). But pKa’s of amino acids can have unusual behavior in active sites !
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pKa = 10 10 9 9 10 10 8.5 10 10 4.7 H Having the charged amino groups close together alters the pKa of the  middle amino group in DET (positive charges close together causes DET  to easily lose a proton). At pH 7, the middle amino group in DET is deprotonated.
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Asp Ser His In the chymotrypsin catalytic triad, the negative charge on  Asp stabilizes the positively charged Histidine. This allows the Histidine to accept a proton from Serine in  the catalytic mechanism. + H H - -
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true  of  enzyme  catalysts ? a) They change the equilibrium constant for a  reaction, to favor the products. a) They increase the activation energy for conversion  of substrate to product. a) To be effective, enzymes must be present in 
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This note was uploaded on 06/20/2011 for the course CHEM 369 taught by Professor Hoffman during the Spring '11 term at University of Texas.

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ch369_sp11_enz_2_notes - uncatalyzed reaction catalyzed...

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