Reversible loss of crystallinity on photobleaching purple membrane in the presence of hydroxylamine

Structural changes of purple membrane during photobleaching in the presence of hydroxylamine were monitored using atomic force microscopy (AFM). The p rocess of bleaching was associated with the disassembly of the purple membr ane crystal into smaller crystals. Imaging steps of the photobleaching prog ress showed that disassembly proceeds until the sample is fully bleached an d its crystallinity is almost lost. As revealed from high resolution AFM to pographs, the loss of crystallinity was initiated by loss of lattice formin g contact between the individual bacteriorhodopsin trimers. The bacteriorho dopsin molecules, however, remained assembled into trimers during the entir e photobleaching process. Regeneration of the photobleached sample into int act purple membrane resulted in the reassembly of the bacteriorhodopsin tri mers into the trigonal lattice of purple membrane. The data provide novel i nsights into factors triggering purple membrane formation and structure. (C ) 2000 Academic Press.