alliinasesubstrate

Alliinase substrate refers to the substrates of the enzyme alliinase (also called alliin lyase), a thiol-oxidoreductase found in many Allium species such as garlic. The primary substrate is alliin, a sulfur-containing amino acid sulfoxide known as S-allyl-L-cysteine sulfoxide. Related S-alk(en)yl cysteine sulfoxides found in Allium plants, such as isoalliin and methiin, can also serve as substrates, though with varying efficiency.

The substrate set is defined by structural features common to S-alk(en)yl cysteine sulfoxides: a cysteine-derived backbone with a sulfoxide group and an allyl or other alk(en)yl substituent. Upon tissue damage, alliinase encounters these substrates and catalyzes a β-elimination reaction, producing allyl sulfenic acid and dehydroalanine. Two molecules of allyl sulfenic acid rapidly condense to form allicin, a diallyl thiosulfinate that is largely responsible for garlic’s aroma and many of its antimicrobial properties. Allicin itself is unstable and decomposes further into a variety of sulfur-containing compounds.

Biological and practical significance: alliinase activity links plant defense to tissue disruption, generating reactive sulfur species that deter pathogens and herbivores. In culinary and pharmacological contexts, the alliinase–substrate system explains why crushing garlic yields allicin and subsequent sulfur volatiles with antimicrobial activity. The study of alliinase substrates informs both plant biochemistry and the development of garlic-derived therapeutics and flavors.