title: Discharged photoprotein obelin: fluorescence peculiarities.
abstract: Photoprotein obelin, the enzyme-substrate complex of polypeptide with 2-hydroperoxycoelenterazine, is responsible for bioluminescence of marine hydroid Obelia longissima. Addition of Ca(2+) to the photoprotein triggers the bioluminescent reaction with light emission. The product of the bioluminescent reaction--enzyme-bound coelenteramide--is a fluorescent protein called 'discharged' obelin. It is stable and highly fluorescent. The paper considers dependence of its light-induced fluorescence on Ca(2+) concentration. Increase of Ca(2+) concentration enhanced the fluorescence intensity of discharged obelin; the dependence was found as linear in double logarithmic coordinates at Ca(2+) concentration range 10(-7)-10(-6) M, both in excitation and emission spectra. The spectra were divided into components; contributions of the components to experimental excitation and emission spectra depended on Ca(2+) concentration. The data suggest enzymatic conformational transition in discharged obelin at approximately 5 x 10(-7) M of Ca(2+) concentration. Spectra variations were attributed to acidity changes of discharged obelin chromophore (coelenteramide) in its fluorescent state S(1)*.
authors.affiliation: Institute of Biophysics SB RAS, Krasnoyarsk 660036, Russia. nbelogurova@mail.ru
authors.forename: Nadezhda V
authors.initials: NV
authors.lastname: Belogurova
authors.forename: Nadezhda S
authors.initials: NS
authors.lastname: Kudryasheva
mesh_terms: D000818:Animals; D044482:Benzeneacetamides / Q000737:chemistry; D002118:Calcium / Q000737:chemistry; D020134:Catalytic Domain; D037402:Hydrozoa / Q000201:enzymology; D008164:Luminescent Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011719:Pyrazines / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013050:Spectrometry, Fluorescence
chemical_list: D044482:Benzeneacetamides; D008164:Luminescent Proteins; D011719:Pyrazines; D011994:Recombinant Proteins; C542661:coelenteramide; C010497:obelin; D002118:Calcium