First insights into the mode of action of a “lachrymatory factor synthase” – Implications for the mechanism of lachrymator formation in Petiveria alliacea, Allium cepa and Nectaroscordum species

A mechanistic study of an enzyme that reacts with the sulfenic acid produced from petiveriin by the alliinase in Petiveria alliacea L. to yield the P. alliacea lachrymator (phenylmethanethial S-oxide) showed the protein to be a dehydrogenase. This dehydrogenase activity contrasts with that of the lachrymatory factor synthase (LFS) found in onion, which should be classified as an isomerase. [Display omitted] ► The mechanism of lachrymatory sulfine formation in Petiveria alliacea was studied. ► The sulfine is formed by hydride abstraction from phenylmethanesulfenic acid. ► It is concluded that the P. alliacea LFS is a dehydrogenase, whereas the LFS from onion ( Allium cepa) is an isomerase. A study of an enzyme that reacts with the sulfenic acid produced by the alliinase in Petiveria alliacea L. (Phytolaccaceae) to yield the P. alliacea lachrymator (phenylmethanethial S-oxide) showed the protein to be a dehydrogenase. It functions by abstracting hydride from sulfenic acids of appropriate structure to form their corresponding sulfines. Successful hydride abstraction is dependent upon the presence of a benzyl group on the sulfur to stabilize the intermediate formed on abstraction of hydride. This dehydrogenase activity contrasts with that of the lachrymatory factor synthase (LFS) found in onion, which catalyzes the rearrangement of 1-propenesulfenic acid to ( Z)-propanethial S-oxide, the onion lachrymator. Based on the type of reaction it catalyzes, the onion LFS should be classified as an isomerase and would be called a “sulfenic acid isomerase”, whereas the P. alliacea LFS would be termed a “sulfenic acid dehydrogenase”.