Chemical Biology 3OA3, September 2009
Page 57
7.
I
NTERPRETING YOUR DATA
The following pieces of information will help you interpret your data.
(1)
Active site serine
Esterases use a Ser residue as an active site nucleophile to form a covalent acyl-enzyme
intermediate, and release the first product, HO-R
2
(Scheme 2).
In the second step, water acts as a
nucleophile to complete the reaction, releasing R
1
-COOH.
Thus, we know that if a diester
substrate is cleaved at a particular site, then that ester group was located near the active site Ser
during catalysis.
R
1
O
R
2
O
Scheme 2.
HO
R
2
R
1
O
O
esterase
HO
esterase
R
1
COOH
H
2
O
esterase
HO
(2)
Hydrophobic substrates
Esterases tend to favour hydrophobic (non-polar) substrates.
The hydrophobic
interactions between non-polar groups are relatively non-specific - the tightest binding (and
highest rate) is achieved with substrates that fill the active site to the greatest extent without
causing steric clashes.
Substituents that are too large or too small will be worse substrates.
Substituents with polar functional groups may require you to consider electronic effects (electron
This is the end of the preview.
Sign up
to
access the rest of the document.
- Fall '11
- RickTroendle
- Chemistry, Organic chemistry, Enzyme, pH, Catalysis, ester group, Esterases
-
Click to edit the document details