The metabolic fate of the nigrostriatal toxin l-methyl-4pheny1-1, 2, 3, 6-tetrahydropyridine (MPTP) has been examined in rat and rabbit liver mitochondrial and rabbit liver microsomal preparations. The mitochondrial preparations rapidly oxidized MPTP, in a pargyline- sensitive reaction, to a polar material that was shown to contain the 1-methyl-4- phenylpyridinium species as the principal product. NADPH-supplemented microsomal ...