The Phenylalanine/Hydroxycinnamte Pathway

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The phenylalanine/hydroxycinnamte pathway: The phenylalanine/hydroxycinnamte pathway starts with metabolism of Phe and called general phenylpropanoid metabolism. The reactions involving formation of hydroxycinnamates and their activated forms (CoA thoesters and 1-O-acylglucosides) fall under the purview of phenylalanine/hydroxycinnamte pathway [Figure 17.3]. First enzyme of hydroxycinnamte pathway is phenylalanine ammonia lyase (PAL; 4.3.1.24) which catalyses the non-oxidative deamination of Phe to trans-cinnamate (first phenylpropane) structure. The trans-cinnamate is further reduced to p-coumarate (4-coumarate) by the action of an NADPH dependent cinnamate-4-hydroxylase (1.14.13.11). This p-coumarate (alternatively called hydroxycinnamate)…show more content…
4. Condensation: It is a sort of side-chain elongation where malonyl CoAs are attached to hydroxycinnamates, CO2 is liberated and acetate unit gets joined and further the output products are flavonoids. [Place Figure 17.3 here] The phenylpropanoid group is one of the most diverse group having great variations in their structure and functions. The colour producing phenylpropanoid products are flavonoids and anthocyanins produced by condensation reactions. Synthesis of flavonoids, anthocyanins and anthocynidins: Flavonoids are coloured compounds imparting colours ranging from red, yellow, scarlet, violet, and blue and so on. There are more than 5000 different known flavonoids. Flavonoids are C15 aglycone skeletons in the arrangement C6-C3-C6 with two aromatic rings connected by a three-carbon bridge. Interestingly, this structure originates of two separate biosynthetic pathways. The bridge and one aromatic ring (ring B) is founded by a phenyl¬propanoid unit biosynthesized from p-coumaryl-CoA (refer formation of p-coumaryl CoA from Phe; above). The six carbons of the other aromatic ring (ring A) originate

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