 Norepinephrine itself can further be converted into epinephrine by the enzyme phenylethanolamine "N"-methyltransferase with "S"-adenosyl-L-methionine as cofactor.In mammals, norepinephrine is rapidly degraded to various metabolites.The initial step in the breakdown can be catalyzed by either of the enzymes monoamine oxidase (mainly monoamine oxidase A) or COMT.