Aspects of intramolecular light energy and electron transfer will be discussed for three protein cofactor complexes, whose three-dimensional structures have been elucidated by x-ray crystallography: Components of light harvesting cyanobacterial phycobilisomes, the purple bacterial reaction centre, and the blue multi-copper oxidases. A wealth of functional data is available for these systems which allow specific correlations between structure and function and general conclusions about light energy and electron transfer in biological materials to be made.
Abbreviations PBS, phycobilisomes, light harvesting organelles peripheral to the thylakoid membrane in cyanobacteria, which carry out oxygenic photosynthesis and have photosystems I and II; PE, PEC, PC, APC, phycoerythrin, phycoerythrocyanin, phycocyanin, allophycocyanin, biliprotein components in PBS with covalently attached tetrapyrrole (bilin) pigments; PS I, II, photosynthetic reaction centers in chloroplasts and cyanobacteria; RBP, retinol binding protein; BBP, bilin (biliverdin IXγ) binding protein in Pieris brassicae; Rps. viridis, bacteriochlorophyll-b containing purple bacterium carrying out anoxygenic photosynthesis; RC, reaction centre; C, H, L, M, the four subunits of the reaction centre from Rps. viridis: the cytochrome c subunit (C), with 4 haems displaying two redox potentials (c553, c558) is located on the periplasmic side of the membrane; the L- and M-, subunits are integrated in the membrane and their polypeptide chains span the membrane with 5 α-helices each; labelled A, B, C, D, E, they bind the bacteriochlorophyll-b (BChl-b or BC), bacteriopheophytin-b (BPh-b or BP), menaquinone-9 (QA), ubiquinone-9 (UQ, QB) and Fe2+ cofactors; the subscriptsP,A,M,L, indicate pair, accessory, M-, L-subunit association, respectively; the H-subunit, is located on the cytoplasmic side and its N-terminal α-helical segment (H) spans the membrane; P680, P960, primary electron donors in PS II and the RC of Rps. viridis, respectively, indicating the long wavelength absorption maxima; P*, D*, electronically excited states of P and D LHC, light harvesting complexes; LHa,b, light harvesting protein pigment complexes in BChl-a,b containing bacteria; Car, carotenoids; Sor, Soretbands of Chl and BChl; PCY, plastocyanin, electron carrier in the photosynthetic apparatus, of plants; LAC, laccase, oxidase in plants and fungi; AO, ascorbate oxidase, oxidase in plants; CP, ceruloplasmin, oxidase in mammalian plasma
1Nobel Lecture given on 8th December, 1988, by Professor Robert Huber and published in Les Prix Nobel 1988, printed in Sweden by Norstedts Tryckeri, Stockholm, Sweden, 1989, republished here with the permission of the Nobel Foundation, the copyright holder.