title: Circular dichroism of the photoreceptor pigment oxyblepharismin.
abstract: Circular dichroism (CD) was used to study the structure of oxyblepharismin (OxyBP), the photoreceptor chromophore for the photophobic response of the blue form of Blepharisma japonicum. Both the chromophore associated to its native protein and the free chromophore in ethanol solution were investigated. CD spectra in the far-UV range indicate that OxyBP induces a slight increase in the alpha-helix content of the protein matrix. CD spectra in the near-UV and visible region of the spectrum show that OxyBP adopts a chiral conformation with a preferential geometry not only when associated to its protein matrix, but also when isolated and dissolved in ethanol. This experimental result is related to the existence of a high-energy interconversion barrier between two enantiomeric structures of the molecule and discussed on the basis of an asymmetric biosynthesis of its precursor, blepharismin.
authors.affiliation: Istituto di Biofisica CNR-Sezione di Pisa, 56124 Pisa, Italy. osvaldo.pieroni@pi.ibf.cnr.it
authors.forename: Osvaldo
authors.initials: O
authors.lastname: Pieroni
authors.forename: Pascal
authors.initials: P
authors.lastname: Plaza
authors.forename: Mathilde
authors.initials: M
authors.lastname: Mahet
authors.forename: Nicola
authors.initials: N
authors.lastname: Angelini
authors.forename: Giovanni
authors.initials: G
authors.lastname: Checcucci
authors.forename: Manuela
authors.initials: M
authors.lastname: Malatesta
authors.forename: Monique M
authors.initials: MM
authors.lastname: Martin
authors.forename: Francesco
authors.initials: F
authors.lastname: Lenci
mesh_terms: D000818:Animals; D016798:Ciliophora / Q000737:chemistry; D002942:Circular Dichroism; D015394:Molecular Structure; D010569:Perylene / Q000031:analogs & derivatives* / Q000737:chemistry / Q000145:classification; D010786:Photoreceptor Cells / Q000737:chemistry*; D020283:Photoreceptors, Microbial / Q000737:chemistry / Q000145:classification; D010860:Pigments, Biological / Q000737:chemistry / Q000145:classification; D011485:Protein Binding; D011487:Protein Conformation; D015800:Protozoan Proteins / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet
chemical_list: D020283:Photoreceptors, Microbial; D010860:Pigments, Biological; D015800:Protozoan Proteins; C505951:oxyblepharismin; D010569:Perylene