The proposed project is a direct continuation and expansion of studies conducted under NSF project exploiting findings in that investigation. One aspect of the project centers on the oxidation of the neurotoxic amine MPTP (N- methyl-4-phenyl-1,2,3,6- tetrahydropyridine) and of its structural analogs by the two forms of monoamine oxidase )MAO), which are known to exist in mammalian mitochondria, and the reversible inhibition of MAO A and B by the pyridinium oxidation products of MPTP analogs. These tertiary amines are of profound interest to biochemists, pharmacologists, and neurobiologists because in humans, subhuman primates, and certain other species they induce neurological conditions essentially identical with those seen in Parkinson patients. Expression of their neurotoxic action is initiated by the 4-electron oxidation of these tetrahydropyridines by either or both forms of brain MAO. A study of the structural requirements of MAO A and MAO B for rapid oxidation of these tertiary amines has revealed completely unexpected facets of the specificities of these enzymes and has already yielded major new information concerning their catalytic properties. Many more classes of structural analogs remain to be tested with these different enzyme forms. Another aspect of the program explores further the mechanism of neuronal death caused by the pyridinium compounds formed by MAO. It is known that they inhibit the respiration of mitochondria by blocking the reoxidation of the flavoprotein NADH dehydrogenase by Coenzyme Q. m Structure-function studies under this proposed program should greatly increase our understanding of the requirements for the interaction of MPP+ analogs with NADH dehydrogenase. We plan to expand our recent experiments which have demonstrated that the classical inhibitors of NADH dehydrogenase (rotenone, piericidin, and barbiturates) bind at the same site and compete with MPP+ and its analogs. Extension of these studies to photoaffinity analogs of MPP+ and congeners is expected to establish which of the subunits of the complex NADH dehydrogenase molecular are close to the Q reduction site.
