D- and L-Amino Acids
Also known as: D-amino acid · L-amino acid · stereochemistry · chirality · retro-inverso
Amino acids come in mirror-image L and D forms; swapping in D-residues can make a peptide far more stable to enzymes.
Most biological amino acids are the "L" (left-handed) form; their mirror images are the "D" form. Because enzymes are shaped to recognise L-residues, peptides built with D-amino acids resist enzymatic breakdown far better.
Peptide designers exploit this: substituting D-residues, or using a full "retro-inverso" design (a reversed sequence of D-amino acids), can dramatically extend half-life while preserving shape. FOXO4-DRI is a well-known retro-inverso example.
RELATED TERMS
Amino Acid
The building-block molecules of peptides and proteins; each contributes one residue to the chain.
Half-Life
The time for a compound’s concentration to fall by half — a key determinant of dosing frequency in research.
FOXO4-DRI
A designed peptide (FOXO4 D-Retro-Inverso) studied as a senolytic — selectively clearing senescent "zombie" cells in ageing research.
Analog
A peptide deliberately modified from a natural sequence to improve stability, selectivity or potency.
Amino-Acid Sequence
The specific order of amino-acid residues in a peptide — its "primary structure" — which dictates shape and activity.
Educational content, not medical advice. All products supplied for research purposes only — not for human consumption.