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Figure 1 | BMC Evolutionary Biology

Figure 1

From: Evolution of specifier proteins in glucosinolate-containing plants

Figure 1

Glucosinolates and glucosinolate hydrolysis. A. Examples of structures of aliphatic glucosinolates (1, 4-methylthiobutylglucosinolate), aromatic (i.e. Phe-derived) glucosinolates (2, benzylglucosinolate), and indolic glucosinolates (3, indol-3-ylmethylglucosinolate). B. Using allylglucosinolate (4, aliphatic side chain with terminal double bond) as an example, the hydrolysis by myrosinase (a) is shown that leads to the formation of an isothiocyanate upon spontaneous rearrangement of the aglycone (b) or to the formation of alternative products (c-e). The ability to form organic thiocyanates depends on structural requirements of the glucosinolate side chain and the presence of thiocyanate-forming protein (TFP; c). Epithiospecifier proteins (ESPs) promote the formation of epithionitriles upon hydrolysis of glucosinolates with a terminal double bond (d), but do not support organic thiocyanate formation. Simple nitriles are formed at acidic pH, in the presence of ferrous ions or due to the action of nitrile-specifier proteins (NSPs; e). If a glucosinolate does not fullfill the structural requirements for epithionitrile formation, ESPs promote the conversion of the aglycone to the simple nitrile. In a similar way, TFPs support epithionitrile or simple nitrile formation upon myrosinase-catalyzed hydrolysis of glucosinolates that do not allow organic thiocyanate formation.

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