Is there elliptic distortion in the light harvesting complex 2 of purple bacteria?

ABSTRACT

Single molecule spectroscopy (SMS) revealed an unusually large Gap between two major exciton peaks of the B850 unit of light harvesting complex 2 (LH2), which could be explained assuming elliptic distortion or k = 2 symmetry modulation in the site excitation energy. On the basis of extensive simulation of the SMS data and ensemble line shape, we found that uniform modulation of k = 2 symmetry cannot explain the dependence of intensity ratios on the Gap of the two major peaks, which are available from SMS, nor the ensemble line shape. Alternative models of disorder with k = 1 and k = 2 symmetry correlation are shown to reproduce these data reasonably well and can even explain the Gap distribution when it is assumed that the lower major peak in the SMS line shape is an intensity weighted average of k = 1- and k = 0 states.