The size of LH1 determined by the ratio of bacteriochlorophyll/bacteriopheophytin in purple bacteria containing LH1 only

Abstract

The structure of the RC-LH1 complex, where a LH1 ring surrounds closely a single RC, raised the question as to the mechanism of quinone transfer from the RC to the membranes. Here we reconsidered the models of RC-LH1 complex by determining the BChl/BPhe ratios in several species of purple bacteria containing only LH1. The resultant ratios obtained by normal-phase HPLC analyses showed some variation in the range of BChl/BPhe = 12 - 24, e.g., Rps. viridis showed a ratio of BChl b/BPhe b = 14 and Rsp. rubrum showed a ratio of BChl aGG/BPhe a = 18. Based on the well-accepted molar ratio BChl/BPhe = 2 in the RC of purple bacteria and the recently reported stoichiometry of BChl/LH1 = 32 found in Rsp. rubrum, the results were summarized by LH1/RC = 3/4 - 4/3, which cannot always support the model according to which a ring of LH1 made of 16 a ß subunits surrounds a single RC. We will discuss the possible models of RC-LH1 complex which can interpret the variation.