title: Reactive ground-state pathways are not ubiquitous in red/green cyanobacteriochromes.
abstract: Recent characterization of the red/green cyanobacteriochrome (CBCR) NpR6012g4 revealed a high quantum yield for its forward photoreaction [J. Am. Chem. Soc. 2012, 134, 130-133] that was ascribed to the activity of hidden, productive ground-state intermediates. The dynamics of the pathways involving these ground-state intermediates was resolved with femtosecond dispersed pump-dump-probe spectroscopy, the first such study reported for any CBCR. To address the ubiquity of such second-chance initiation dynamics (SCID) in CBCRs, we examined the closely related red/green CBCR NpF2164g6 from Nostoc punctiforme. Both NpF2164g6 and NpR6012g4 use phycocyanobilin as the chromophore precursor and exhibit similar excited-state dynamics. However, NpF2164g6 exhibits a lower quantum yield of 32% for the generation of the isomerized Lumi-R primary photoproduct, compared to 40% for NpR6012g4. This difference arises from significantly different ground-state dynamics between the two proteins, with the SCID mechanism deactivated in NpF2164g6. We present an integrated inhomogeneous target model that self-consistently fits the pump-probe and pump-dump-probe signals for both forward and reverse photoreactions in both proteins. This work demonstrates that reactive ground-state intermediates are not ubiquitous phenomena in CBCRs.
authors.affiliation: Department of Chemistry and ‡Department of Molecular and Cellular Biology, University of California, Davis , One Shields Avenue, Davis, California 95616.
authors.forename: Che-Wei
authors.initials: CW
authors.lastname: Chang
authors.forename: Sean M
authors.initials: SM
authors.lastname: Gottlieb
authors.forename: Peter W
authors.initials: PW
authors.lastname: Kim
authors.forename: Nathan C
authors.initials: NC
authors.lastname: Rockwell
authors.forename: J Clark
authors.initials: JC
authors.lastname: Lagarias
authors.forename: Delmar S
authors.initials: DS
authors.lastname: Larsen
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D046937:Nostoc / Q000378:metabolism; D052980:Phycobilins / Q000737:chemistry; D010798:Phycocyanin / Q000737:chemistry; D011789:Quantum Theory; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D052980:Phycobilins; D011994:Recombinant Proteins; D010798:Phycocyanin; C011069:phycocyanobilin