The core light-harvesting LH1 protein fromRhodospirillum rubrumcan dis-sociate reversibly in the presence ofn-octyl-b-d-glucopyranoside into smal-ler subunit forms, exhibiting a dramatic blue-shift in absorption. During this process, two main species are observed: a dimer that absorbs at 820 nm (B820) and a monomer absorbing at 777 nm (B777).