(2S)-2-aminobutanoate + formaldehyde => 2-ethyl-L-serine
(2s)-2-aminobutanoate + formaldehyde => 2-ethyl-l-serine
(2S)-2-aminobutanoate + formaldehyde => 2-ethyl-L-serine
(2s)-2-aminobutanoate + formaldehyde => 2-ethyl-l-serine