Glucosinolate thioglucoside

A major proportion of the glucosinolate hydrolysis products formed upon myrosinase cleavage in some plants are nitriles. In vitro, nitrile formation associated with myrosinase-catalyzed hydrolysis is enhanced at low pH (pH<3) and in the presence of ferrous ions. In vivo, protein factors in addition to myrosinase may be responsible for nitrile formation. If the glucosinolate side chain has a terminal double bond, the sulfur released from the thioglucosidic bond may be captured by the double bond and an epithionitrile is formed.9 This reaction takes place only in plants that possess a protein factor known as epithiospecifier protein (ESP). ESP activities have been identified in several species of the Brassicaceae and shown to influence the outcome of the myrosinase-catalvzed hydrolysis reaction although they have no hydrolytic activity by themselves.10 12 The mechanism by which ESPs promote epithionitrile formation is not known. 

Glucosinolates (Figure 8.11) are a class of about 100 naturally occurring thioglucosides that are characteristic of the Cruciferae and... 

Several of the putative intermediates contain a C-N double bond, presenting the possibility of geometrical isomers. The actual configuration of these intermediates has not been examined but is assumed to be the same as observed in the final glucosinolate (Poulton and Mpller, 1993). L-Cys-teine may serve as an efficient source of the sulfur atom in the thioglucoside moiety. 

Glucosinolate, mustard oil thioglucoside, mustard oil glucoside a natural plant product with the structure shown in Fig. 1. G. are particularly abundant... 

Thioglucoside ghicohydrofame, fi-lkloglucosi-dose, myrosin, myrosutase, sm rimase, sinigrase (EC 3.2.3.1) a plant enzyme responsible for the conversion of glucosinolates into isothiocyanates (see Glucosinolate). 

Glucosinolates are thioglucosides. They contain a C=N-group substituted with sulfate and a residue R in anti position, as well as a sulfur atom connected with a /3-D-glucopyranosyl moiety (Table 44). At hydrolysis they liberate glucose, sulfate and an unstable aglycon. From the latter isothiocyanates (mustard oils), thiocyanates, nitriles, or cyanoepithioalkanes may be formed. 

In plant tissue, glucosinolates are accompanied by the enzyme myrosinase (thioglucoside glucohydrolase), which catalyses their decomposition. Myrosinase is a globular glycoprotein with a relative molecular weight of 140 kDa, consisting of several isoenzymes. 

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