L-methionine
L-2-Amino-4methyltiobutiric acid

C5H11NO2S

It's a amino acid.

Catabolism of methionine, threonine, isoleucine and valine (3D)
Synthesis of aspartate, methionine, lysine and threonine (3D)
Aminoacyl-tRNA biosynthesis (Kyoto University)