H-Tyr(3-I)-OH is an inhibitor of tyrosine hydroxylase (Ki = 0.39 M) and an intermediate in the synthesis of thyroid hormones.

L-Citrulline is an amino acid derived from ornithine in the catabolism of proline or glutamine and glutamate or from l-arginine via arginine-citrulline pathway.

Sphingosine-1-phosphate (S1P) is an agonist for S1P1-5 receptors and a ligand for GPR3, GPR6, and GPR12. As an intracellular second messenger, it mobilizes Ca2+ and acts as an extracellular ligand for G-protein coupled receptors.