Analysis of Flash Photolysis Data by a Global Fit With Multi‐exponentials–i. Determination of the Minimal Number of Intermediates in the Photocycle of Bacteriorhodopsin by the ‘Stability Criterion’

A major problem in establishing a kinetic scheme for photo‐induced reaction sequences is the determination of the unknown number of important intermediates. It is shown that in addition to the χ 2 ‐value and the distribution of the residuals obtained from a least‐squares fit of the experimental curves by a sum of exponentials, the stability of the apparent rates towards an increase of the number of exponentials with arbitrary test values can be used as an additional criterion. Experimental data describing the photocycle of bacteriorhodopsin after the appearance of intermediate K ( t > 1 μs) are analysed with the described algorithm. It is found that 5 exponentials are necessary and sufficient for the fit.