Figure 7.

B850 BChls. (A) The ring of 18 B850 molecules viewed from the periplasmic side of the complex, with Mg–Mg distances of 9.2 and 9.3 Å shown. (B) Three pairs of B850 BChls in a spacefill representation. (C) Structural model of two adjacent B850 dimer binding sites showing hydrogen bonds between LH2 α-Tyr44, α-Tyr45, and a C3-acetyl carbonyl on each BChl. α-Ser27 is hydrogen-bonded to the C13¹ keto on ring E. Different shades differentiate the αβ heterodimers, with the α-polypeptide in yellow; β-polypeptide, blue; and B850, green. B800, phytyl tails, and carotenoids have been removed for clarity.