The objective of this project is to use primarily an electrochemical approach to study the fundamental molecular processes that underlie the light- mediated sensory (visual) and energy (photosynthetic) transduction in model retinal protein membranes. We take advantage of the chemical similarity between rhodopsin (visual pigment), bacterio-rhodopsin (a light-driven proton pump) and halorhodopsin (a light-driven chloride pump) to explore possible common designs in these proteins for different functions. We use a tunable voltage clamp method to analyze site-specific electric signals from membranes reconstituted from normal and chemically modified retinal proteins. We proposed a regulatory mechanism of visual transduction based on the early receptor potential. We also discovered site-specific signals from halorhodopsin membranes that are analogous to the B1 and the B2 component of bacteriorhodopsin membranes (named H1 and H2, respectively). Our preliminary results show that the H2 component is highly sensitive to aqueous chloride concentration. Keywords: Photochemical reactions; Molecule molecule interactions; Membrane; Pigment; Integral protein; Bacteriorhodopsin; Rhodopsin; Halorhodopsin; Photoelectric signal; Light-induced rapid charge separation; Vision; Photosynthesis.