The L and D convention for amino acid configuration refers not for the optical exercise in the amino acid by itself but relatively on the optical action in the isomer of glyceraldehyde from which that amino acid can, in concept, be synthesized (D-glyceraldehyde is dextrorotatory; L-glyceraldehyde is levorotatory). This article https://www.supplementsbymail.com/product-category/amino-acids/