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)- right 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 C(-OH)-CH(-NH2)- right CH2-CO- + NH3 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. (EC 4.3.2), the amine-lyases (EC 4.3.3), and other carbon-nitrogen lyases (EC 4.3.99).