Photoaffinity labelling of submitochondrial membranes with the 3-azido analogue of 9-amino-3-chloro-7-methoxyacridine.

9-Amino-3-azido-7-methoxyacridine has been synthesized and shown to be a suitable photoaffinity probe for the site(s) of interaction of 9-amino-3-chloro-7-methoxyacridine with submitochondrial membranes. Both the excitation and emission spectra of the azido analogue covalently bound to membranes in the energized state display distinctive differences from the spectra of labelled, non-energized membranes (i.e., in the absence of oxidizable substrate, or its presence when uncoupler (FCCP) is also present during photolysis). Enzymatic analyses indicate that the probe interacts with the ATPase and the respiratory chain enzymes; energization appears to afford some protection against inactivation. Electrophoresis of the labelled membranes and isolation of their lipid and protein components indicate that the spectral differences are attributable to differing interactions with the lipid components of energized, relative to non-energized, membranes. Similar results have been obtained with the 3-azido analogue of quinacrine (Mueller, D.M., Hudson, R.A. and Lee, C.P. (1982) Biochemistry 21, 1445-1453), which differs significantly, however, in the extent of its interactions with the enzymes of the respiratory chain and the ATPase. These results indicate that the energy-linked fluorescence responses of 9-aminoacridines with submitochondrial membranes arise from direct interactions with membrane components and may involve redistribution of the probe molecules and/or alteration of their microenvironments upon energization.