ch369_sum10_enz_2_notes

ch369_sum10_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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An example of how local structure can alter pKa’s
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pKa = 10 10 9 9 An example of how local structure can alter pKa’s
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pKa = 10 10 9 9 10 10 8.5 An example of how local structure can alter pKa’s
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pKa = 10 10 9 9 10 10 8.5 An example of how local structure can alter pKa’s 10 10 4.7
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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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Hexokinase – catalyzes the 1st step in glycolysis. Many more enzymes coming soon! For example: Many more enzymes this semester, but chymotrypsin is really the only enyzme where we will carefully look at the mechanism.
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Next topic - Rates of enzyme catalyzed reactions.
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This note was uploaded on 08/26/2010 for the course CH 369 taught by Professor Kbrowning during the Spring '07 term at University of Texas at Austin.

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ch369_sum10_enz_2_notes - uncatalyzed reaction catalyzed...

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