LIGHT-INDUCED DENATURATION OF BACTERIORHODOPSIN JUST ABOVE MELTING-POINT OF 2-DIMENSIONAL CRYSTAL

The denaturation kinetics of bacteriorhodopsin induced by light irradi ation was measured in the temperature range between 80 and 86 degrees C, which was just above the melting point of the two-dimensional cryst al composed of bacteriorhodopsin molecules in the purple membrane. Bac teriorhodopsin was stable in the dark but gradually denatured under th e irradiation of visible light longer than 520 nm. Analyzing the time course of the light-induced denaturation phenomenon, the kinetic const ant of the denaturation from a photointermediate state was estimated. The temperature dependence of the kinetic constant lead to the effecti ve activation energy of about 41 kcal/mol. The stability of a photoint ermediate state was discussed on the basis of the light-induced denatu ration behavior.