EC 4.3 Carbon-nitrogen lyases
This subclass contains the enzymes that release ammonia or one of its derivatives, with the formation of a double bond or ring. Some catalyse the actual elimination of the ammonia, amine or amide, e.g.
>CH-CH(-NH-R)- → >C=CH- + NH2-R
Others, however, catalyse elimination of another component, e.g. water, which is followed by spontaneous reactions that lead to breakage of the C-N bond, e.g. as in EC 18.104.22.168 (L-serine ammonia-lyase), so that the overall reaction is:
i.e., an elimination with rearrangement. The sub-subclasses of EC 4.3 are the ammonia-lyases (EC 4.3.1), lyases acting on amides, amidines, etc. (amidine-lyases; EC 4.3.2) and the amine-lyases (EC 4.3.3).