Chemistry Reference
In-Depth Information
Im
O
Zn
+2
+
Im
O
C
Im
H
O
Im
O
Zn
+2
Im
O
C
O
-
Im
H
H
2
O
Im
O
+
H
+
Zn
+2
+
H
Im
O
O
C
O
-
Im
H
Im = imidazole
FIGURE 12.4
The main features of the mechanism of carbonic anhydrase.
His
142
HN
HN
His
69
HN
His
69
N
N
N
O
O
O
Zn
II
Zn
II
Zn
II
OH
2
Glu
72
OH
2
OH
2
Glu
165
Glu
72
O
O
O
N
N
N
HN
HN
His
196
HN
His
196
His
146
thermolysin
carboxypeptidase A
carboxypeptidase B
FIGURE 12.5
Active sites of thermolysin and carboxypeptidases A and B.
Bovine carboxypeptidase A was only the third protein, after myoglobin and lysozyme, to have its three-
dimensional structure solved at high resolution. The active site zinc is bound to His-69, Glu-72, and His-196
(
Figure 12.5
), and to a water molecule. The zinc-bound water molecule is itself hydrogen bonded to Glu-270.
Despite extensive experimental data, the mechanism of carboxypeptidase still remains controversial. Two major
