Chemistry Reference
In-Depth Information
11
In the proposed mechanism of hydrolysis (
16
), the carboxylate anion of
13
-
15
or
acetyl Phe is recognized by the guanidinium ion, and the Cu(
II
) center subsequently
hydrolyzes the amide group. Both the electrostatic interaction between carboxylate and
guanidinium ions and the Cu(
II
)-catalyzed amide cleavage would be facilitated by the
microenvironment provided by polystyrene.
In carboxypeptidase A [52, 53], the active-site Zn(
II
) ion plays essential catalytic roles
and the guanidinium of Arg-145 recognizes the carboxylate anion of the substrates,
thus making the enzyme an exopeptidase. Important features of carboxypeptidase A
reproduced by
11
include the essential catalytic action of a metal ion and participation
of a guanidinium group in substrate recognition, so that this polymer biocatalyst hy-
drolyzes unactivated amides, and exhibits selectivity toward amide bonds adjacent to
carboxylate groups in the substrate.
Multinuclear metal centers are present in the active sites of several metalloproteases.
A catalytic polymer with peptidase activity containing trinuclear active sites has been
prepared [51] using
17
. Upon treatment of
17
with excess NaH, at least three of the six
Figure 3.9 pH dependence of k
o
for
hydrolysis of 13 (
), 14 (
), and 15 (
*
)
10
-4
M
) promoted by 11
(C
o
= 1.08m
M
)at50
8
C. Unlike the
carboxyl-containing amides, the neutral
amide (12) was not hydrolyzed.
(S
o
= 1.96
