title: Resonance Raman analysis of the Pr and Pfr forms of phytochrome.
abstract: Resonance Raman vibrational spectra of the Pr and Pfr forms of oat phytochrome have been obtained at room temperature. When Pr is converted to Pfr, new bands appear in the C = C and C = N stretching region at 1622, 1599, and 1552 cm-1, indicating that a major structural change of the chromophore has occurred. The Pr to Pfr conversion results in an 11 cm-1 lowering of the N-H rocking band from 1323 to 1312 cm-1. Normal mode calculations correlate this frequency drop with a Z----E isomerization about the C15 = C16 bond. A line at 803 cm-1 in Pr is replaced by an unusually intense mode at 814 cm-1 in Pfr. Calculations on model tetrapyrrole chromophores suggest that these low-wavenumber modes are hydrogen out-of-plane (HOOP) wagging vibrations of the bridging C15 methine hydrogen and that both the intensity and frequency of the C15 HOOP mode are sensitive to the geometry around the C14-C15 and C15 = C16 bonds. The large intensity of the 814-cm-1 mode in Pfr indicates that the chromophore is highly distorted from planarity around the C15 methine bridge. If the Pr----Pfr conversion does involve a C15 = C16 Z----E isomerization, then the intensity of the C15 HOOP mode in Pfr argues that the chromophore has an E,anti conformation. On the basis of a comparison with the vibrational calculations, the low frequency (803 cm-1) and the reduced intensity of the C15 HOOP mode in Pr suggest that the chromophore in Pr adopts the C15-Z,syn conformation.
authors: Department of Chemistry, University of California, Berkeley 94720.
authors: S P
authors: SP
authors: Fodor
authors: J C
authors: JC
authors: Lagarias
authors: R A
authors: RA
authors: Mathies
mesh_terms: D002523:Edible Grain / Q000378:metabolism; D008027:Light; D008958:Models, Molecular; D010798:Phycocyanin / Q000378:metabolism; D010834:Phytochrome / Q000302:isolation & purification / Q000378:metabolism*; D011487:Protein Conformation; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman / Q000379:methods
chemical_list: D010798:Phycocyanin; D010834:Phytochrome