Cyanogenic glucosides biosynthesis

Figure 3.8 Metabolic cross-talk between glucosinolate and cyanogenic glucoside biosynthesis in transgenic Arabidopsis plants (according to Kristensen et a ., 2005).

The amount of these unknown cyanogens could be significantly enhanced by applying osmotic stress to the cultures. In addition, l-(4 -hydroxvphenyl)-2-nitroethane was present in the cultures. This compound is thought to be a side-product of cyanogenic glucoside biosynthesis (see Section 3.2.4). 

KOCH, B.M., SIBBESEN, O., HALKIER, B.A., SVENDSEN, I., M0LLER, B.L., The primary sequence of cytochrome P450tyr, the multifunctional N-hydroxylase catalyzing the conversion of L-tyrosine to /7-hydroxyphenylacetaldehyde oxime in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench, Arch. Biochem. Biophys., 1995,323, 177-186. 

CYP79s in the Biosynthesis of Cyanogenic Glucosides and Glucosinolates 233 The Oxime-Metabolizing Enzyme as Branch Point between the Cyanogenic... 

ANDERSEN, M.D., M0LLER, B.L., Cytochromes P450 from Cassava (Manihot esculenta Crantz) catalyzing the first steps in the biosynthesis of the cyanogenic glucosides linamarin and lotaustralin cloning, functional expression in Pichia pastoris and substrate specificity of the isolated recombinant enzymes, J. Biol. Chem., 2000,275, 1966-1975. 

For example, the anti (25) and syn (4-hydroxyphenyl)acetaldoximes, 26, are established intermediates in the biosynthesis of the cyanogenic glucoside of sorghum, dhurrin, 27, and the biochemical pathway for its production in the plant was shown to originate in the A -hydroxylation of tyrosine, in the presence of NADPH/O2, as outlined in equation 15". It was further suggested that the Z (syn) isomer, 26, is utilized preferentially over E(anti )-25 in the subsequent biosynthesis of dhurrin, 27. The same authors provided evidence that the biosynthesis of the aldoxime, 25, proceeds via an aci-nitro containing intermediate, R R C=N(0)0H, that is positioned between Af-hydroxytyrosine and anti-25 in the biosynthetic pathway . 

Due to homologies in structures and biosynthesis, some minor groups of natural products seem to be related to cyanogenic glucosides. These compounds, i.e. cyanogenic lipids, nitrile- and nitro-compounds, are briefly presented in this chapter. 

Biosynthesis of dhurrin in sorghum plays an important role as a model system for obtaining further insight into the enzymology and molecular biology of the biosynthesis of cyanogenic glucosides. 

Figure 3.7 Biosynthesis of cyanogenic glucosides. The biosynthetic pathway of cyanogenic glucosides exemplarily is mentioned for dhurrin. The biosynthesis is performed by the two multi-functional cytochrome P450 enzymes and a UDP-glucosyltransferase. All three enzymes are joined together in a metabolon located in the ER-membrane (according to Nielsen et al., 2008).

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