(2S,3R)-diaminobutanoate + fumarate => N(3)-1,2-dicarboxyethyl-diaminobutanoate
(2s,3r)-diaminobutanoate + fumarate => n(3)-1,2-dicarboxyethyl-diaminobutanoate
(2S,3R)-diaminobutanoate + fumarate => N(3)-1,2-dicarboxyethyl-diaminobutanoate
(2s,3r)-diaminobutanoate + fumarate => n(3)-1,2-dicarboxyethyl-diaminobutanoate