Canavanine is an amino acid that resembles arginine. It is found in some legumes, particularly in the seeds. Canavanine serves as a nitrogen store and as a defense mechanism. Some worms tRNA ligase enzymes that normally attach arginine to its tRNA will instead attach the structurally similar canavanine, which is then incorporated into proteins in place of arginine. This can make these proteins function erratically. Canavanine is poisonous to organisms that cannot distinguish it from arginine.