Benserazide and carbidopa as substrates of catechol- O-methyltransferase: New mechanism of action in Parkinson's disease

The DOPA-decarboxylase (aromatic- l-amino acid decarboxylase) inhibitors benserazide, its active metabolite 2,3,4-trihydroxybenzylhydrazine and carbidopa are substrates of highly purified catechol- O-methyltransferase. The affinity and maximal velocity of both benserazide and trihydroxy-benzyl hydrazine are extremely favourable implying that these compounds may compete as substrates for catechol- O-methyltransferase with l-DOPA. These results are discussed in the light of the ability of benserazide to cause further elevation of plasma l-DOPA than carbidopa and the use of these compounds in Parkinson's disease.