Isolation and characterization of a light harvesting complex II lacking the γ-polypeptide from Rhodobacter capsulatus

Abstract

Extraction of membranes isolated from the wild-type strain 37b4 of Rhodobacter capsulatus with Na 2CO 3 removed quantitatively the 14000 M r γ-polypeptide from the light-harvesting complex II (LHC II). The same procedure was used to extract the γ-polypeptide from the isolated LHC II. The LHC II free of the γ-polypeptide ( M r 14000) and containing the pigment-binding polypeptides α ( M r 10000) and β ( M r 8000) showed the same absorption spectrum as LHC II in the presence of the γ-polypeptide. Reaction center (RC) bleaching of the extracted and untreated membranes showed the same kinetics. Furthermore, kinetics of RC bleaching at different light intensities were identical in extracted and unextracted preparations, indicating that the LHC II lacking γ-polypeptide was able to transfer excitation energy efficiently to the LHC I-RC complexes. This efficient coupling was also confirmed by low temperature (77 K) fluorescence spectroscopy. The results indicate that the γ-polypeptide is not required for the function of the LHC II.