PHOTOISOMERIZATION QUANTUM YIELD AND APPARENT ENERGY CONTENT OF THE KINTERMEDIATE IN THE PHOTOCYCLES OF BACTERIORHODOPSIN, ITS MUTANTS D85N, R82Q, AND D212N, AND DEIONIZED BLUE BACTERIORHODOPSIN

The quantum yield of photoisomerization and the energy content of the K intermediate in the photocycle of bacteriorhodopsin and its mutants D85N, R82Q, and D212N and deionized blue bR were measured. Transient o ptical absorption and photoacoustic spectroscopy with excitation using 400 fs laser pulse were combined to obtain results. The spectroscopic characteristics of the excited state, the J and K intermediates in th e photocycle of the mutants, and deionized blue bR were determined. Th e presence of both 13-cis and all-trans isomers in the ground state of light-adapted D85N, R82Q, and D212N and deionized blue bR makes extra ction of the quantum yield for each isomer difficult. Thus, only avera ge values of the quantum yield for these samples were determined. The replacement of charged groups in the vicinity of the retinal Schiff ba se was found to decrease the rate of the photoisomerization by up to 3 0 times, but with no signficant change in either the apparent quantum yield of the photoisomerization or the energy stored in the K intermed iate. The results are discussed in terms of the different models for t he excited and ground state potential surfaces of the retinal configur ation in bacteriorhodopsin.