The behaviour of aryl pyrrolines with monoamine oxidase.

We have examined the effects of monoamine oxidase (MAO) on two pyrrolines, 1-methyl-3-phenyl-delta 3-pyrroline and its 4-chlorophenyl analogue. They act as substrates but also inhibit the enzyme in a time-dependent manner. This behaviour is similar to that shown by the neural pro-toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydro pyridine (MPTP) which is metabolised by MAO to produce the toxin 4-phenyl pyridinium (MPP+). The end product of the oxidation of the pyrrolines appears to be the corresponding pyrrole. The latter were found to inhibit MAO reversibly. The aryl pyrrolines bear close structural resemblance to MPTP and probably generate a pyrrolium ion, analogous to MPDP or MPP+, during the oxidation by MAO. Whether pyrrolines or their metabolites might mimic the effects of MPTP on mitochondrial respiration remains an unanswered question.