EFFECT OF MELITTIN ON PHOTOCYCLE AND PHOTOPOTENTIAL OF PURPLE MEMBRANE: SITES OF INTERACTION BETWEEN BACTERIORHODOPSIN AND MELITTIN

Abstract— Purple membrane (PM) suspension and artificial bilayer lipid membranes (BLM) containing PM sheets were treated with melittin. Both the decaying of the photocycle intermediate M412 and proton translocation were inhibited by melittin: The yields and rate of the slow-decaying component of M412 (M412s) together with the proton release and its uptake rate were significantly decreased, but the rate of the fast-decaying component of M412 (M4120 had only slight changes. Relatively high concentrations of melittin could cause aggregation in PM suspensions. Addition of melittin to a BLM solution increased the continuous photopotential signal but decreased the transient signal. We suggest that there might exist strong interactions between melittin and bacteriorhodopsin in addition to the melittin–lipid action. On the other hand, the results also indicate that proton translocation was more likely to be coupled with M412s and both were more sensitive to the changes caused by the melittin–PM interaction than was M412f.