Mechanisms of Enzymes Flashcards Preview

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Flashcards in Mechanisms of Enzymes Deck (8):
1

Proteases
•Proteases are enzymes that cleave ___ ____ by ____
•The resonance stabilized peptide bond is ___ ___ ___ (high activation energies) requiring protease enzymes to cleave the bond.
•Several proteases are involved in the break down of proteins in the ___ ___ of higher organisms. 
 


•Proteases are enzymes that cleave peptide bonds by hydrolysis.



•The resonance stabilized peptide bond is kinetically very stable (high activation energies) requiring protease enzymes to cleave the bond.

•Several proteases are involved in the break down of proteins in the digestive system of higher organisms. 
 

2

Chymotrypsin
•Cleaves peptide bonds selectively on the ____ terminal side of the ___ ____ amino acids such as ____ ____ ____ ____. Determines specificity of the enzyme.
•Chymotrypsin uses _____interactions as a catalytic strategy to stabilize the ___ _____

•Consists of _ peptide chains linked by ___ ____
•Initially synthesized as a ___ ____ ______, activated  by cleavage to yield __ chains. 
•Overall forms a _____structure.
•Posses a catalytic ___residue (______) in the active site located on the surface of protein.
•Serine residue is ________ to _____ which in turn is_____ to ______ in the active site.
•The 3 amino acids in the active site are known as the ________ ____.
 


•Cleaves peptide bonds selectively on the carboxyl terminal side of the large hydrophobic amino acids such as tryptophan, tyrosine, phenylalanine, and methionine. Determines specificity of the enzyme.
•Chymotrypsin uses covalent interactions as a catalytic strategy to stabilize the transition state. 

•Consists of 3 peptide chains linked by disulfide bonds.
•Initially synthesized as a single chain chymotrypsinogen, activated  by cleavage to yield 3 chains. 
•Overall forms a spherical structure.
•Posses a catalytic serine residue (Ser 195) in the active site located on the surface of protein.
•Serine residue is H-bonded to Histidine, which in turn is H-bonded to Aspartic acid in the active site.
•The 3 amino acids in the active site are known as the catalytic triad. 
 

3

Catalytic Mechanism of Chymotrypsin


•Formation of a____ _____ ____ intermediate carrying a ____charge.
•Negative charge is stabilized by ___ ____
•This site is known as the____ ____
•Stabilizes the transition state. (lowers the activation energy of the reaction)
 


•Formation of a unstable tetrahedral covalent intermediate carrying a negative charge.
•Negative charge is stabilized by electrostatic interactions.
•This site is known as the oxyanion hole.
•Stabilizes the transition state. (lowers the activation energy of the reaction)
 

4

Specificity of Chymotrypsin


•____ pocket (known as the _ pocket) enables residues ___ ___ ___ and ___ to __ in and ____ the peptide bond into the ___ ____ for ____

•This determines the ____ of the enzyme. 
 


•Hydrophobic pocket (known as the S pocket) enables residues tryptophan, tyrosine, phenylalanine, and methionine fit in and orient the peptide bond into the active site for cleavage.

•This determines the specificity of the enzyme. 
 

5

Specificity of other serine proteases


•Trypsin cleaves at the peptide bond after residues with ___, ____ charged side chains (____ ____)
•Elastase cleaves at the peptide bond after amino acids with ____ side  chains (___ ____).
•S pockets of these enzymes defines the specificity.
•In trypsin, ___# is present at the bottom of the S pocket in place of a serine residue in chymotrypsin. The aspartate residue ____ and___ a positively charged arginine or lysine residue in the substrate.
•In elastase, two residues at the top of the pocket in chymotrypsin and trypsin are replaced with ____(#).
•These residues close off the mouth of the pocket so that only ____ ____ chains may enter.
 


•Trypsin cleaves at the peptide bond after residues with long, positively charged side chains (arginine and lysine).
•Elastase cleaves at the peptide bond after amino acids with small side  chains (alanine and serine).
•S pockets of these enzymes defines the specificity.
•In trypsin, Asp 189 is present at the bottom of the S pocket in place of a serine residue in chymotrypsin. The aspartate residue attracts and stabilizes a positively charged arginine or lysine residue in the substrate.
•In elastase, two residues at the top of the pocket in chymotrypsin and trypsin are replaced with valine (Val 190 and Val 216).
•These residues close off the mouth of the pocket so that only small side chains may enter.
 

6

Catalytic Mechanisms of Cysteine, Aspartyl and Metalloproteases


•Cysteine proteases- ____, activated by a ____ , plays the role of the nucleophile that attacks the peptide bond. Example - ____

•Aspartyl proteases – A ____ of ______ residues that act together to allow a ____ ____ to attack the peptide bond. Example -____

•Metalloproteases - ___ ___ activates a ____ ____to act as a nucleophile to attack the peptide ___ ___. Example - ______
 


•Cysteine proteases- Cysteine, activated by a histidine , plays the role of the nucleophile that attacks the peptide bond. Example - Caspases•Aspartyl proteases – A pair of aspartic acid residues that act together to allow a water molecule to attack the peptide bond. Example - Renin

•Metalloproteases - metal ion activates a water molecule to act as a nucleophile to attack the peptide carbonyl group. Example - Angiotensin converting enzyme (ACE)


 

7

Use of Protease Inhibitors in Disease


•Protease inhibitors are similar to the structures of the ___ ____
•These inhibitors used as drugs must be specific for ___ enzyme without _____
•Example - ____, inhibitor of the _____ ____


•Protease inhibitors are similar to the structures of the substrate peptides.
•These inhibitors used as drugs must be specific for one enzyme without inhibiting other proteins within the body.
•Example - Crixivan, inhibitor of the HIV protease.
 

8

Summary


•The ___ ____is important for the function of serine proteases.
•The ___ ____ define the specificity of each serine protease.
•Catalytic mechanisms of cysteine, aspartyl and metalloproteases ___ from one another.
 


•The catalytic triad is important for the function of serine proteases.
•The S pockets define the specificity of each serine protease.
•Catalytic mechanisms of cysteine, aspartyl and metalloproteases differ from one another.