Chemistry Reference
In-Depth Information
Figure 6.18 Active site of
D
-fructose 1,6-biphosphate 1-phosphatase.
metal centers [4-7, 83]. There has been considerable, prolonged interest in under-
standing the mechanism of hydrolysis of phosphate monoesters and the role of simple
mononuclear [84-87] and dinuclear [88-90] metal complexes in the hydrolysis reac-
tion. Since the hydrolysis of phosphate mono- and diesters often follows different me-
chanisms [19], it is important to study the mechanisms of both reactions. In the ab-
sence of added catalysts, monoesters and diesters generally hydrolyze by dissociative
and associative mechanisms, respectively.
The structure of
D
-fructose 1,6-biphosphate 1-phosphatase has been reported [82].
Proposedly, the two metal centers at the active site of the enzyme are bridged by the
substrate phosphate monoester, and a metal hydroxide is involved in the hydrolysis
(Figure 6.18).
Sargeson et al. [91] showed that a phosphate monoester bridging two Co(
III
) centers
is rapidly hydrolyzed by a neighboring metal hydroxide (
27
) (Figure 6.19). The metal-
bound phosphate is hydrolyzed (4
10
-1
s
-1
at 25
8
C) about eight orders of magnitude
more rapidly than the free phosphate (2
10
-9
s
-1
at 25
8
C). More recently, we showed
that the phosphate monoester in
28
[92] is hydrolyzed (5
10
-2
s
-1
at 25
8
C) about 11
orders of magnitude more rapidly than the free phosphate (5
10
-13
s
-1
at 25
8
C) (Fig-
ure 6.19). Double Lewis acid activation may not provide as much rate acceleration for
hydrolyzing phosphate monoesters as for hydrolyzing phosphate diesters (
24
). In
Figure 6.19 Models of
D
-fructose 1,6-biphosphate 1-phosphatase.
