Pyrrole-2-carboxylic acid was first identified as a degradation product of sialic acids then as a derivative of the oxidation of the D-hydroxyproline isomers by mammalian D-amino acid oxidase.

D(-)-2-Aminobutyric acid is the substrate of D-amino acid oxidase.

N-Acetyl-L-alanine is a substrate for Guanine nucleotide-binding protein G(I)/G(S)/G(O) gamma-2 subunit Myelin basic protein GTP-binding nuclear protein Ran Tropomyosin alpha 4 chain HIV-1 Rev binding protein 2 Xaa-Pro dipeptidase Thymosin beta-10 Actin-like protein 3 Alanine aminotransferase Serine/threonine protein phosphatase PP1-beta catalytic subunit 10 kDa heat shock protein (mitochondrial) Calmodulin and Beta-1-syntrophin.