title: Effect of the removal of the COOH-terminal region of bacteriorhodopsin on its light-induced H+ changes.
abstract: Removal of the COOH-terminal region of bacteriorhodopsin by digestion with trypsin or papain reduces the yield of light-induced H+ release by 50-70%. The rate of H+ release is not affected significantly, but the half time of H+ uptake increases almost twofold. However, there is no effect on the photocycle of bacteriorhodopsin as judged by the yield and decay kinetics of the M412 photointermediate. The H+:M ratio in enzyme-digested membranes is approximately 0.4-0.8, whereas untreated membranes have a H+:M ratio of approximately 2. Purple membrane sheets stored in distilled water at 4 degrees C for prolonged periods also have a low H+:M ratio, probably due to protease activity associated with bacterial contamination. Electrophoresis on sodium dodecylsulfate-polyacrylamide gels showed that both the enzyme-treated and the stored purple membrane samples have a higher electrophoretic mobility compared to the fresh preparation. The reduction in molecular weight can be accounted for by the loss of several residues from the COOH-terminal portion of the bacteriorhodopsin. We propose that the COOH-terminal region is partially responsible for the high yield of H+ release by the purple membrane.
mesh_terms: D001436:Bacteriorhodopsins / Q000378:metabolism*; D002268:Carboxypeptidases / Q000494:pharmacology; D043422:Carboxypeptidases A; D002338:Carotenoids / Q000378:metabolism*; D006217:Halobacterium / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D010206:Papain / Q000494:pharmacology*; D014357:Trypsin / Q000494:pharmacology*
chemical_list: D002338:Carotenoids; D001436:Bacteriorhodopsins; D002268:Carboxypeptidases; D043422:Carboxypeptidases A; D014357:Trypsin; D010206:Papain