The enzyme homocysteine desulfhydrase (EC 4.4.1.2) catalyzes the chemical reactionL-homocysteine + H2O = hydrogen sulfide + NH3 + 2-oxobutanoate (overall reaction) (1a) L-homocysteine = hydrogen sulfide + 2-aminobut-2-enoate (1b) 2-aminobut-2-enoate = 2-iminobutanoate (spontaneous) (1c) 2-iminobutanoate + H2O = 2-oxobutanoate + NH3 (spontaneous)