Enzyme Mechanisms Flashcards
what catalyzes the hydrolytic cleavage of pepetide bonds
Serine proteases
What are serine proteases found in the pancreas
trypsin
chymotrypsin
Elastase
which molecule has about 3 polypeptides linked with disulfide bond
Chymotrypsin
Chymotrypsin with cleave to whcih side chain
hydrophobic/aromatic side chain, Trp, Phe, Tyr
what amino acid forms the catalytic triad in chymotrypsin
His, Ser, Asp
chymotrypsin has how many mechanism
2-step, acylation and deacylation
which protease catalyze peptide hydrolysis but not via direct addition of water to the peptide bond
Chymotrypsin
protein cleave peptide bonds but also
slow cleave esters
the first step pf chymotryopsin results to
p-nitrophenylacetate, fast reaction
what can deactivate a serine residue
DIFP (diisopropyl phosphofluoridate
what makes Ser a better nucleophile
H-bonded chain
When His 57 abstract proton from Ser 195, it is a
general base
HIs 57 is stabilized by
Asp 102 carboxylate
The second step of chymotrypsin reeaction mechanism
- nucleophilic attack of alkoxide ion on peptide carbonyl carbon leads to tetrahedral intermediate (acyl-enzyme)
*negatively charged O stabilized by oxyanion hole through Ser & Gly
H bond to Gly 193 only occur in this intermeiate
what mechanism is when alkoxide ion on peptide carbonyl leads to tetrahedral intermediate
Transition State
what happens in step 3 of chymotrypsin reaction
tetrahedral intermediate collapses reforming C=O and breaking C-N bond
hist 57 acts a a general acid to protonate amino group make it a better leaving group
what happens in step 4
Acyl-enzyme intermediate remains
N-terminal peptide is bound to covaltny bound to ser 195
first part is released
what happens in step 5
this 57 acts as a general base again and abstract proton from water
OH- acts a nucleophile and attacks C=O
what happens in step 6
OH- Attack on C=O leads to tetrahedral intermediate
negative charge on O stabilized by oxyanion hole
what haooens in step 7
tetrahedral intermediate collapses, reforming C=O
C-O bonds is broken as His acts as general acid to facilitate displacement to Ser
HIV protease uses which amino acid
aspartate
active site asparate
aspartyl protease
does water directly attach the peptide bond in HIV protease or covalent enzyme-susbtrate complex true/fasle
yes
HIV protease cleaves amino acid
Phe
pro
