Biomedical Engineering Reference
In-Depth Information
NH
2
CH
2
CH
COOH
N
Tryptophan
Tryptophanase (
E.coli
)
N
Indole
Naphthalene dioxygenase
(cloned)
H
OH
N
HOH
cis-indole-2, 3-dihydrodiol
Spontaneous
O
O
OH
OH
O
N
O
N
NH
2
Indoxyl
Isatin
Isatic acid
Air oxidation
Air oxidation
O
O
N
N
N
Fig. 14.16
The biosynthesis of indigo
in
E. coli
and the formation of
alternative end products.
N
O
O
Indigo
Indirubin
above. With both indigo and melanin, yields are
improved by increasing the levels of cofactors. Also,
in the case of indigo biosynthesis, it is necessary to
engineer the tryptophan synthase gene. The reason
for this is that indole is an intermediate in the
biosynthesis of tryptophan (Fig. 14.15). However,
normally it is not free in the cytoplasm but remains
trapped within the tryptophan synthase complex.
By modifying the
trpB
gene, encoding the subunit of
tryptophan synthase, it was possible for the indole
to be released for conversion by the dioxygenase
(Murdock
et al.
1993).
One disadvantage of the new route to indigo is
that one of the intermediates in its synthesis,
indoxyl, can undergo an alternative spontaneous
oxidation to isatin and indirubin. The latter com-
pound is an isomer of indigo with similar dyeing
properties, but instead of being blue it is a deep
