500 MHz 1H NMR of chlorophylls in the major light-harvesting chlorophyll-protein complex of photosystem II

500 MHz 1H NMR spectra were obtained of solutions containing oligomeric and monomeric forms of Chl a/b-P2, the major light-harvesting chlorophyll a/b-protein complex of photosystem II, isolated from thylakoid membranes of barley (Hordeum vulgare). Oligomers showed only a broad unresolved spectrum, but for monomers several downfield-shifted chlorophyll proton resonances were observed, assigned to the alpha and beta methine protons and the formyl proton of Chl-b. Identifying the observed shifts as ring-current shifts, these NMR data can be matched with previously obtained optical data confirming the trimeric arrangement of Chl-b in Chl a/b-P2 protein, with a distance between the chromophore centers of approximately 12 A.