1QKO:
reference: High-resolution X-ray structure of an early intermediate in the bacteriorhodopsin photocycle., Edman K, Nollert P, Royant A, Belrhali H, Pebay-Peyroula E, Hajdu J, Neutze R, Landau EM, Nature 1999 Oct 21;401(6755):822-6. PMID: 10548112

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