Bacterial antenna complex proteins are the main light-absorbing components in photosynthetic bacteria. In photosynthetic purple bacteria the antenna complexes function as light-harvesting systems that absorb light radiation and transfer the excitation energy to the photosynthetic reaction centres. The antenna complexes are generally composed of two types of polypeptides (alpha and beta chains) which are arranged in a ring-like fashion creating a cylinder that spans the membrane; the proteins bind two or three types of bacteriochlorophyll (BChl) molecules and different types of carotenoids depending on the species. Both the alpha and the beta chains of antenna complexes are small proteins of 42 to 68 residues which share a three-domain organization. They are composed of a N-terminal hydrop