SPECIFICITY OF PYRIDINIUM INHIBITORS OF THE UBIQUINONE REDUCTION SITES IN MITOCHONDRIAL COMPLEX-I

Dual binding sites for pyridinium-type inhibitors in bovine heart mito chondrial complex I have been proposed (Gluck, Ri. R., Krueger, M. J., Ramsay, R. R., Sablin, S. O., Singer, T. P., and Nickles, W. J. (1994 ) J. Biol. Chem. 269, 3167-3174). The marked biphasic nature of the do se-response curve for inhibition of the enzyme by ethyl-4-[2-(p-tert-b utylbenzyl)propyl]-pyridinium) makes this compound the first selective inhibitor of the two sites (Miyoshi, H., Inoue, M., Okamoto, S., Ohsh ima, M., Sakamoto, K., and Iwamura, H. (1997) J. Biol. Chem. 272, 1617 6-16183). Modifications of the structure of MP-6 show that a tert-buty l group on the benzene ring, a methyl group attached to the pyridine n itrogen atom, para-substitution pattern in the pyridine ring, and the presence of a branched structure in the spacer moiety are important fo r the selective inhibition. On the basis of the structural specificity , we synthesized a selective inhibitor, MP-24 2-methyl-2-(p-tert-butyl benzyl)propyl]pyridinium), which elicits greater selectivity. Characte rization of the inhibitory behavior of MP-24 provided further strong e vidence for the dual binding sites model.