REDETERMINATION OF THE QUANTUM YIELD OF PHOTOISOMERIZATION AND ENERGYCONTENT IN THE K-INTERMEDIATE OF BACTERIORHODOPSIN PHOTOCYCLE AND ITSMUTANTS BY THE PHOTOACOUSTIC TECHNIQUE

Data obtained previously in our lab for the quantum yield retinal phot oisomerization and the energy content of the K-intermediate formed in the bacteriorhodopsin and its mutants (bR) photocycle are reexamined u sing time-resolved transient spectroscopy and laser-induced photoacous tic spectroscopy. In the present experiment both nanosecond and subpic osecond laser pulses are used for excitation, with different reference compounds. From these new results it can be concluded that using CoCl 2 as a reference compound in the photoacoustic experiment with subpico second laser pulses gives a large amount of prompt heat release result ing from multiphoton absorption processes. This results in an overesti mated energy content of the K-intermediate of bR and its mutants. Usin g different reference compounds, the corrected values are 40 +/- 10 kJ /mol, which is in agreement with previously reported values. The appar ent quantum yield and energy content values (for each of the isomeric compositions) of the mutants D212N, D85N, R82Q, A53G, W182F, V49A, dei onized blue bR, and acid purple bR are also recalculated using bR as a reference compound and are similar to those of bR. (Phi is in the ran ge 0.55-0.65, and E-K is in the range 40-50 kJ/mol.) The relative inse nsitivity of the apparent average quantum yield value is discussed.