– (+)-Biotin 4-amidobenzoic acid is a substrate of biotinidase, which cleaves biotin amide to give biotin in vivo. Biotin is an essential coenzyme for certain carboxylases and is used to modify histones and regulate gene transcription. Biotinidase has key roles in intestinal absorption of biotin, the transport of biotin in plasma, and in the regulation of histone biotinylation. (+)-Biotin 4-amidobenzoic acid is hydrolyzed by biotinidase to release 4-aminobenzoic acid (PABA), which can be quantified by either fluorescent or colorimetric methods. This approach is used in biotinidase activity assays in newborn screening protocols to evaluate biotinidase deficiency.