Abstract: To elucidate the surface charge and membrane binding characteristics of peripheral light harvesting complex 2 (LH2) from different purple bacteria, as well as the relationship between its spectral structure and function characteristics, the effects of solubilization time, salting out concentration and anion exchange chromatography elution gradient on the purification results and characteristics of LH2 from different species were investigated. The results showed that the solubilization time and salting out concentration of the LH2 (A-LH2) from Rhodobacter azotoformans were lower than those of the LH2 (P-LH2) from Rhodopseudomonas palustris, whereas the anion exchange chromatography elution gradient of A-LH2 was higher than that of P-LH2, indicating that A-LH2 had stronger membrane binding ability and was easy to dissociated from membrane, besides, A-LH2 had strong hydrophobicity and more negative surface charge. Compared with that in P-LH2, the characteristic absorption peaks of BChl a Qy in A-LH2 blue shifted to 798 and 848 nm, and the elution volume of A-LH2 in molecular sieve chromatography was slightly smaller, indicating that the molecular size of A-LH2 was larger. Pigment composition analysis showed that 3,4-didehydrorhodopin (conjugated double bonds N=12) was the main carotenoid in P-LH2 whereas spheroidene (conjugated double bonds N=10) was the main carotenoid in A-LH2. Raman spectra analysis indicated that spheroidene adopted a planar conformation bound to proteins in A-LH2, and the shorter conjugated double bonds and an extended conformation were beneficial for energy transferring in A-LH2. This study provided a method for comparing the membrane binding ability and surface charge of LH2 among different species (strains). Meanwhile, the comparative analysis of the LH2 from different purple bacteria could provide theories foundation for the construction of artificial photoelectric conversion device or artificial photosynthetic hydrogen production system by using LH2 from purple bacteria.

Key words: light harvesting complex 2 (LH2), Rhodobacter azotoformans, Rhodopseudomonas palustris, separation and purification, spectral analysis