decarboxylated

3-(Methylthio)propionic acid (4-Thiapentanoic acid) is one of the metabolites of methionine (especially of D-methionine). Cultures of Streptomyces lincolnensis accumulated 3-methylthioacrylic acid in amounts directly related to the concentration of methionine in the medium. The first intermediate in the pathway may be the keto acid, which is then oxidatively decarboxylated to 3-methylthiopropionic acid.

L-DOPA (Levodopa) is an amino acid precursor of dopamine with antiparkinsonian properties. It is a prodrug converted to dopamine by DOPA decarboxylase and can cross the blood-brain barrier. In the brain, levodopa is decarboxylated to dopamine, stimulating dopaminergic receptors and compensating for depleted endogenous dopamine in Parkinson's disease. To ensure adequate concentrations reach the central nervous system, levodopa is administered with carbidopa, a decarboxylase inhibitor that does not cross the blood-brain barrier, reducing peripheral decarboxylation and increasing CNS dopamine delivery.