The third M intermediate is formed under stationary light irradiation in the photocycle of bacteriorhodopsin

We found the third M intermediate (Mslow2) with a lifetime as long as that of N on the bacteriorhodopsin (bR) photocycle in alkaline suspension. While the reported slow-decaying M, Mslow1, forms under intense pulsed or continuous (stationary) light irradiation, Mslow2 needs both lights. Mslow1 is a cooperative product (Tokaji et al.) with a quantum yield that depends on both light intensities, whereas Mslow2 is formed from the species accumulated by the continuous light. These results show that formation process of Mslow2 is different from that for Mslow1.