phytochlorin and pheophytin-a

Relative bleaching rates of bovine rhodopsin (rod outer segments) in the presence and absence of seven porphyrins and methylene blue were measured under exposure to lambdamax = 675 nm light, using UV-vis spectroscopy. Rate enhancements on the order of up to three times compared to the bleaching of rhodopsin alone where observed. Fluorescence measurements and other data suggests that the porphyrins act as photosensitizers and excite the visual pigment via electron or triplet state energy transfer. These mechanisms suggest that rhodopsin possesses a pocket, proximal to the Schiff base so that porphyrins act as photosensitizers.

Topics: Animals; Cattle; Chlorophyllides; Darkness; Kinetics; Pheophytins; Photobleaching; Photosensitizing Agents; Porphyrins; Rhodopsin; Spectrophotometry, Ultraviolet; Thermodynamics; Vision, Ocular