Cyanogenic glucosides pathway

Halkier, B.A., H.V. Scheller, and B.L. Moller. 1988. Cyanogenic glucosides the biosynthetic pathway and the enzyme system involved. Pages 49-66 in D. Evered and S. Harnett (eds.). Cyanide Compounds in Biology. Ciba Foundation Symposium 140. John Wiley, Chichester. 

Figure 13.2 Biosynthetic pathways of (A) cyanogenic glucosides and (B) glucosinolates. The CYP79s are assumed to catalyze the same reaction in both pathways. It is not known whether the oxime is oxidized to an aci-nitro compound or a nitrile oxide in the glucosinolate pathway.

THE OXIME-METABOLIZING ENZYME AS BRANCH POINT BETWEEN THE CYANOGENIC GLUCOSIDE AND THE GLUCOSINOLATE PATHWAY... 

KAHN, R.A., BAK, S., SVENDSEN, I., HALKIER, B.A., M0LLER, B.L., Isolation and reconstitution of cytochrome P450ox and in vitro reconstitution of the entire biosynthetic pathway of the cyanogenic glucoside dhurrin from sorghum, Plant Physiol., 1997,115, 1661-1670. 

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 . 

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).

Plants are the best organic chemists in nature as evidenced by their ability to synthesize all necessary carbon compounds with carbon dioxide as the sole carbon source and by their ability to synthesize a vast number of natural products. Currently, structures for more than 100,000 different natural products isolated from plants are known, and with time this number will increase into millions. Natural products are classified as phytoanticipins, phytoalexins, and/or attractants. In the last decade, the majority of the biosynthetic pathways responsible for natural product synthesis have been shown to include P450s as key enzymes. Such pathways include the biosynthetic pathways for cyanogenic glucosides, glucosinolates, isoflavonoids, and... 

Figure 12.4. The biosynthetic pathway for the cyanogenic glucoside dhurrin is catalyzed by two multifunctional cytochrome P450s, CYP79A1, and CYP71E1 (P450ox) and by a glucosyltransferase, UGT85B1.

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