a. [ Levo- + DOPA, dihydroxyphenylalanine. ] (Chem. & Biochem.) A substance used as a therapy for Parkinson's Disease; the L form of Dopa; L-dihydroxyphenylalanine; L-hydroxytyrosine (C9H11NO4); also called L-dopa. In the body it is converted by the enzyme dopa-decarboxylase into dopamine, the form in which it is active in the brain, affecting neural impulse transmission. [ PJC ]