Glucosidases myrosinases

Keywords cyanogenic glycosides glucosinolates non-protein amino acids cytochrome P450 cyanogenesis fj-glucosidase myrosinase mustard oil... 

We have previously developed a protein homology model based on the sequence of aphid myrosinase and templates from plant myrosinase and cyanogenic P-glucosidase.12 These enzymes all adopt the (p/a)8-barrel structure typical of this... 

The myrosinase-glucosinolate system occurs in 16 plant families.17 It is likely that this system evolved from the ancient (and near ubiquitous) cyanogenic glycosides. This hypothesis is supported by the similarity, in sequence and structure, of glucosinolate biosynthetic enzymes and the hydrolytic enzymes (myrosinase or p-glucosidase).18 The biochemistry of these metabolites also indicates a convincing evolutionary relationship.19 Furthermore, on the basis of robust phylogenetic trees,... 

In conclusion, it seems that myrosinase activity is relatively easy (in evolutionary time) to acquire from p-glucosidases. It will be a fascinating challenge to pin down the exact molecular alterations that are responsible for the transition from P-[OJ-glucosidase to p-[S]-thioglucosidase. 

Myrosinases are the only known S-glucosidases. Whereas some myrosinases exhibit a pronounced substrate specificity towards glucosinolates (e.g. MacLeod and Rossiter, 1986 Bernardi et al, 2003), most of these hydrolytic enzymes, myrosinases, accept multiple glucosinolate substrates e.g., Chen and Halkier, (1999). However, the hydrolysis of other S- or 0-glucosides is only poorly catalysed by these enzymes (Lein, 1972 Durham and Poulton, 1990 Bernardi et al, 2003). 

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