Chemical diversity of glucosinolate breakdown products formed upon tissue damage.
Structures of intact glucosinolates (green box) and their potential breakdown products (yellow box) in Arabidopsis are depicted for A) 4-methylsulfinylbutylglucosinolate, B) 3-butenylglucosinolate, C) 2-hydroxy-3-butenylglucosinolate, and D) indol-3-ylmethylglucosinolate. Vertical arrows and enzyme names indicate the biosynthetic link between the glucosinolates in A)-C). Arabidopsis AOP2 corresponds to GSL-ALK in Brassica species. Hydrolysis in the absence of specifier proteins (horizontal arrow, no circle) results in isothiocyanate (R-N=C=S) formation. Non-enzymatic cyclization of the isothiocyanate derived from 2-hydroxy-3-butenylglucosinolate yields goitrin (5-ethenyl-1,3-oxazolidine-2-thione, C). Indol-3-ylmethylisothiocyanate is known to further react to indole-3-carbinol, D). Red circles indicate activity of epithiospecifier protein (ESP) on alkenylglucosinolates (B, D) and on glucosinolates with other aliphatic or indolic side chains (A, D). Blue circles indicate activity of nitrile-specifier proteins (NSPs) (A, B, D). The formation of the simple nitrile from 2-hydroxy-3-butenylglucosinolate by NSPs (white circle) has not yet been demonstrated experimentally.