Trans-4-hydroxy-L-proline is an optically active form of 4-hydroxyproline having L-trans-configuration. It has a role as a mouse metabolite, a plant metabolite and a human metabolite. It is a tautomer of a trans-4-hydroxy-L-proline zwitterion. L-Hydroxyproline, one of the hydroxyproline (Hyp) isomers, is a useful chiral building block in the production of many pharmaceuticals.

L-methionine is the L-enantiomer of methionine. It has a role as a micronutrient, a nutraceutical, an antidote to paracetamol poisoning, a mouse metabolite and a human metabolite. It is a L-alpha-amino acid, a methionine, an aspartate family amino acid and a proteinogenic amino acid. It is a conjugate base of a L-methioninium. It is a conjugate acid of a L-methioninate. It is an enantiomer of a D-methionine. It is a tautomer of a L-methionine zwitterion. L-Methionine is marker of cell viability and estimating proliferative activity. L-Methionine and L-cystine can improve hyperlipidemia by restoring LPL and HSL activities, it also might be a new potential drug for Parkinson's disease treatment.