INHIBITION OF ELECTRON-TRANSPORT THROUGH THE Q(P) SITE IN CYTOCHROME B C(1) COMPLEXES BY ACRIDONES/

4-substituted acridones (9-azaanthracen-10-ones) and, to an even highe r extent, 2-substituted acridones were found to be efficient inhibitor s of isolated cytochrome b/c(1) complexes from either beef heart or th e photosynthetic bacterium Rhodospirillum rubrum. Inhibitory activity in a Quantitative Structure-Activity Relationship (QSAR) could be corr elated to physicochemical parameters like STERIMOLb sigma-Hammett and lipophilicity pi. Maximal inhibitory potency for 2-alkylacridones was achieved at a carbon chain length of 9-10 Angstrom. Oxidant-induced re duction of cytochrome b established that 2-alkylacridones are inhibito rs of the Q(p) rather than the Q(n) site.