Chirality in Biology
611
samples. There have been many investiga-
tions of chiral methyl groups in biochemi-
cal processes.
In a similar way, chiral phosphates, con-
taining
16
O,
17
O, and
18
O, and chiral phos-
phorothioates, containing S,
16
O, and
18
O,
have been utilized in several enzymatic re-
actions. Thus, in the action of adenylate
kinase, a phosphorothioate analog of ATP
was used to show that the reaction pro-
ceeds with overall inversion of conFgura-
tion (±ig. 24). Similarly, with the use of all
three of the oxygen isotopes, glucose phos-
phorylation by hexokinase was also shown
to proceed with inversion of conFguration.
7
Chirality in Biological Structures and
Behavior
7.1
Structures
Chirality occurs in many manufactured
objects (e.g. screws, propellers, shoes) and
Fig. 23
Analysis of chiral acetates. The
Frst reaction is that of malate synthase,
glyoxylate
+
acetyl-CoA
malate (for
simplicity, the samples are shown as
acetate rather than as acetyl-CoA). An
isotope effect dictates removal of
1
Has
shown. The second reaction is that
catalyzed by fumarase – removal of the
elements of water with deFned
trans
stereochemistry. The possible fumarate
products are shown on the last line.
O
H
HOOC
H
+
2
H
COOH
1
H
3
H
R
(a)
O
H
HOOC
H
+
3
H
COOH
1
H
2
H
S
(b)
2
H
3
H
COOH
HOOC
H
OH
3
H
2
H
COOH
HOOC
H
OH
H
COOH
HOOC
3
H
H
COOH
HOOC
2
H
is very common in the world of nature.
When viewed externally, the bodies of
humans and most animals show an overall
bilateral symmetry. A mirror plane can
be imagined at right angles to the body,
thus bisecting the nose and legs. Usually,
this symmetry is imperfect with slight
differences say between the left and the
right hands (the right hands of right-
handed people are usually larger than the
left hands). Irregularities are often seen in
faces. ±aces artiFcially constructed from
twole
f
to
rtwor
igh
ts
ide
sa
rema
rked
ly
Fig. 24
The mechanism of action of
adenylate kinase, EC 2.7.4.3. The
catalyzed reaction is
ATP
+
AMP
=
ADP
+
ADP. ATP is
shown as a phosphorothioate analog
containing
16
O,
18
O, and S (double
bonds are omitted). The ‘‘looped arrow’’
indicates that the reaction involves
inversion of conFguration at the
phosphorous atom.
AMP
+
18
OP
16
O
16
O
S
ADP
16
OP
18
O
16
O
S
ADP
AMP
+
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