This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Degradation/Utilization/Assimilation → Secondary Metabolites Degradation → Nitrogen Containing Secondary Compounds Degradation → Alkaloids Degradation|
Some taxa known to possess this pathway include : Beta vulgaris vulgaris
Expected Taxonomic Range: Caryophyllales
The violet to red betacyanins (e.g. betacyanin biosynthesis) are a subclass of the betalains (see betalamic acid biosynthesis) and occur almost exclusively in the order of Caryophyllales [Strack03, Cai05, Grotewold06]. While the biosyntheses of betacyanins and the closely related betaxanthins (e.g. betaxanthin biosynthesis (via dopaxanthin)) are well studied, almost nothing is known about the degradative metabolization of those compounds.
About This Pathway
Soboleva and coworkers [Soboleva76] first described the enzymatically caused discoloration and breakdown of betacyanins in Beta vulgaris (garden beet) under uptake of oxygen. Since then some progress has been made to identify and characterize the enzyme with special focus on its substrate specificity [Shih81, Elliott83].
The assumption that a peroxidase may be involved in the catabolic oxidation of betacyanins has been corroborated by studying the reaction in Camellia sinensis. The peroxidase was found to oxidize both betanidin and its glucosidic derivative betanin. For the betanin oxidation the peroxidase catalyzed a reaction that yielded a intermediate cyclo-DOPA 5-O-β-D-glucoside dimer, and several oxidized cyclo-DOPA 5-O-β-D-glucoside polymers and betalamic acid [Elliott83, Martinez97a].
The peroxidative oxidation of the aglycon betanidin led to the formation of betanidin quinone. The enzymatic reaction involved was to produce the betanidin radical intermediate which subsequently, by further nonenzymatic dismutation, generated betanidin quinone and betanidin. However, the further catabolism of betanidin quinone or its association with interconnecting pathways remains to be studied in more detail. The peroxidase has been classified as a class III peroxidase located in the vacuole. The much lower efficiency of the peroxidase towards betacyanin glucosides and the known vacuolar localization of β-glucosidases were discussed as interactions of both enzymes indicating a metabolic role of this peroxidase(s) in the metabolization of betacyanins [MartinezParra01].
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