Chemistry Reference
In-Depth Information
(e)
Figure 9.2
(
Continued
)
been obtained for both of the purified reductases. Although several putative
clones that encode these proteins have been isolated, the activity of these clones
has not been verified yet (89, 90).
An acetylesterase then hydrolyzes the acetyl link of acetylnorajmaline to yield
norajmaline. This esterase has been purified from
R. serpentina
cell suspen-
sion cultures, and a full-length clone has been isolated from a cDNA library.
Expression of the gene in tobacco leaves successfully yielded protein with the
expected enzymatic activity (91). In the final step of ajmaline biosynthesis, an
N-methyl transferase introduces a methyl group at the indole nitrogen of noraj-
maline. Although this enzymatic activity has been detected in crude cell extracts,
the enzyme has not been characterized additionally (92).
9.3.3 Ajmalicine and Tetrahydroalstonine
Ajmalicine (raubasine) affects smooth muscle function and is used to help
prevent strokes (93), and tetrahydroalstonine exhibits antipsychotic properties
(Fig. 9.2d) (94). These compounds are found in a variety of plants, including
C. roseus
and
R. serpentina
. A partially purified NADPH-dependent reductase
isolated from a tetrahydroalstonine that produces a
C. roseus
cell line was shown
to catalyze the conversion of cathenamine, a spontaneous reaction product that
