sulphonium

A methylene transfer reaction of an imine by an unstabilised sulphonium ylide can give an aziridine system.

A sulfonium ion, also known as sulphonium ion or sulfanium ion, is a positively charged ion (a "cation") featuring three organic substituents attached to sulfur.

Strictly conserved in the C-terminal motif of the SET domain tyrosine could be involved in abstracting a proton from the protonated amino group of the substrate lysine, promoting its nucleophilic attack on the sulphonium methyl group of the AdoMet cofactor.