11. TITLE (Include Security Classification) Mechanism of Conversion of Light Into Chemical Energy in Bacteriorhodopsin: Identification of Charge Movements and Coupling to Active Site

on reverse if necessary and identify by block number) FIELD GROUP SUB-GROUP biophysical chemistry, bacteriorhodopsin, membrane 08 proteins, Halobacteria, nuclear magnetic resonancej 19. ABSTRACTq~i (Cniu onll rees f eesar-_ 19. ABSTRACT (Continue on reverse if neces bblock num erL Bacte riorhodopsin is the best under-stood transmembrane ion pump. Bacteriorhodopsin creates ca. 100 mV transmembrane poten-tial by pumping protons across its membrane when illuminated by visible light. Visible light isomerizes a small (ca. 300 Dalton) chromophore called retinal which drives protein conformational changes that accomplish the pumping. Pumping occurs in a series of steps, and the intermediate forms can be trapped for study at sufficiently low temperatures. New methods of solid state NMR have recently provided striking new information on the detailed structure of the retinal active site in bacteriorhodopsin. However, the ligh