Crying

 

In July 2017’s journal ACS Chemical Biology, M Golczak and J Silvaroli show what happens when you cut an onion.

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A so-called Lachrymatory Factor (LF) is formed by the release of two chemicals that are released by the cutting of cell walls. One is a sulfenic acid precursor. The other is an enzyme called alliinase which is normally contained within the cells’ vacuoles. Upon release the two react to form something like tear gas.

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garlic, an alliinase enzyme acts on the chemical alliin converting it into allicin. The process involves two stages: elimination of 2-propenesulfenic acid from the amino acid unit (with α-aminoacrylic acid as a byproduct), and then condensation of two of the sulfenic acid molecules.

Reaction scheme for the conversion: cysteine → alliin → allicin

There are a range of similar enzymes that can react with the cysteine-derived sulfoxides present in different species. In onions, an isomer of alliin, isoalliin, is converted to 1-propenesulfenic acid. A separate enzyme, the lachrymatory factor synthase or LFS, then converts this chemical to a potent LF.

But none of this mattered to Roy Orbison

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