- β-thioglucosidases, also known as myrosinases, are the enzymes that are known to hydrolyse which one of the following plant natural products?
(1) Glucosinolates
(2) Terpenoids
(3) Alkaloids
(4) Phenolics
Correct answer: (1) Glucosinolates
β-thioglucosidases (myrosinases) specifically hydrolyze the thio-linked glucose from glucosinolates, releasing glucose and unstable aglycones that rearrange into toxic isothiocyanates, nitriles, or thiocyanates—key plant defense compounds found in Brassicaceae.
Option Analysis
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(1) Glucosinolates — Correct. Myrosinase (EC 3.2.1.147) cleaves the β-thioglucoside bond, activating plant defense upon tissue damage.
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(2) Terpenoids — Incorrect. Terpenoids are isoprenoids hydrolyzed by terpene synthases or hydrolases, not β-thioglucosidases.
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(3) Alkaloids — Incorrect. Alkaloids undergo cytochrome P450 oxidation or other modifications, not thioglucoside hydrolysis.
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(4) Phenolics — Incorrect. Phenolics involve phenylpropanoid pathways with enzymes like PAL and CHS, unrelated to thioglucosidase activity.
Myrosinase enzymes hydrolyze glucosinolates into bioactive breakdown products like isothiocyanates, providing chemical defense in cruciferous plants, with the reaction triggered by tissue damage that mixes compartmentalized enzyme and substrate.
