The glucosinolates

Peptides are short chains of amino acids. By combining in various ways, two or more of the over 20 amino acids that are made by ail cells, a very large amount of chemical diversity can be generated. Some species of simple organisms such as the bacteria and the cyanobacteria make a number of distinct peptides, each species producing a different mixture. Some of these molecules have been shown to possess biological activity in certain test systems hence these peptides could be considered as NPs. Interestingly, the biosynthesis of these peptides has been compared, as has the biosynthesis of other NPs (see Chapter 5), with nature s version of the chemist s attempts to maximise the production of chemical diversity.  

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Louda, S. M. and Rodman, J. E. 1983a. Ecological patterns in the glucosinolate content of a native mustard, Cardamine cordifolia, in the Rocky Mountains. J. Chem. Ecol. 9 397-422. 

GiAMOUSTARis A and MITHEN R (1995) The effect of modifying the glucosinolate content of leaves of oilseed rape (Brassica-napus ssp oleifera) on its interaction with specialist and generalist pests . Annals Appl Bio, 126, 347-63. 

SMITH T K, LUND E K and JOHNSON I T (1998) Inhibition of dimethylhydrazine-induced aberrant crypt foci an induction of apoptosis in rat colon following oral administration of the glucosinolate sinigrin , Carcinogenesis, 19, 267-73. 

VAN DOORN H E, VAN DER KRUK G C, VAN HOLST G-J, RAAIJMAKERS-RUIJS N C M E, POSTMA E, GROENEWEG B and JONGEN w H F (1998) The glucosinolates sinigrin and progoitrin are important determinants for taste preference and bitterness of Brussels sprouts , J Sci Food Agric, 78 30-38. 

These reactions to 4-methylthiobutyl glucosinolate, the precursor for sulforaphane formation, have been extensively studied in Eruca sativa (arugula, rocket).64 A gene controlling variation in the glucosinolates of Arabidopsis is part of the methionine elongation pathway just described.65... 

Figure 13.1 Degradation of glucosinolates. Hydrolysis is catalyzed by myrosinases and gives rise to different degradation products dependent on the structure of the glucosinolate side chain and the hydrolysis conditions. (I) isothiocyanates, the major product at pH >7 (II) nitriles, the major product at pH <4 (ID) thiocyanates, produced from 2-propenyl-, benzyl-, and 4-methylthiobutylglucosinolates (IV) oxazolidine-2-thiones, produced from glucosinolates with P-hydroxylated side chains, (V) epithionitriles, produced in the presence of epithiospecifier proteins.

Figure 13.2 Biosynthetic pathways of (A) cyanogenic glucosides and (B) glucosinolates. The CYP79s are assumed to catalyze the same reaction in both pathways. It is not known whether the oxime is oxidized to an aci-nitro compound or a nitrile oxide in the glucosinolate pathway.

THE OXIME-METABOLIZING ENZYME AS BRANCH POINT BETWEEN THE CYANOGENIC GLUCOSIDE AND THE GLUCOSINOLATE PATHWAY... 

Figure 13.5 Metabolic engineering of oxime-derived natural products in Arabidopsis plants. Up- and downregulation of endogenous as well as exogenous CYP79s provides a powerful tool for alteration of the glucosinolate profiles and introduction of novel glucosinolates, as well as for engineering oxime-derived natural products.

Cruciferous species, in which the glucosinolates are biologically active compounds (44), have been studied in both of the latter categories. In Australia, allelopathy has been associated with introduced crucifers such as Brassica tournefortii Gouan (wild turnip) and a more complete study has been made of Camelina sativa (L.) Grants (false flax). 

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