title: Ca2+-specific fluorescence changes in N-dansylaminoethyl-labelled oncomodulin.
abstract: Rat oncomodulin (isoelectric point (pI) = 3.9) and homologous carp parvalbumin (pI = 3.95) was labelled at Cys-18 which is located in the AB loop, with the fluorescent reagent N-dansylaziridine. The fluorescence spectrum of the labelled parvalbumin was insensitive to both Mg2+ and Ca2+ binding. In contrast the dansyl fluorescence emission spectrum of labelled oncomodulin was quenched approximately 20% by Ca2+ in the presence of physiological concentrations of Mg2+. Approximately 90% of the Ca2+-induced fluorescence quenching was complete at a Ca2+/dansyl-S-aminoethyloncomodulin ratio of approximately 1. The labelled oncomodulin was insensitive to Mg2+ binding. The present study indicates that oncomodulin, unlike parvalbumin, undergoes a large Ca2+-specific perturbation that can be felt over the entire molecule. In addition this Ca2+-specific perturbation appears to be complete upon occupation of only one metal-binding site.
mesh_terms: D000818:Animals; D001388:Aziridines; D001389:Azirines; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002347:Carps; D003545:Cysteine / Q000378:metabolism; D003619:Dansyl Compounds; D004577:Electron Probe Microanalysis; D005456:Fluorescent Dyes; D009363:Neoplasm Proteins / Q000378:metabolism*; D010320:Parvalbumins / Q000378:metabolism; D051381:Rats
chemical_list: D001388:Aziridines; D001389:Azirines; D002135:Calcium-Binding Proteins; D003619:Dansyl Compounds; D005456:Fluorescent Dyes; D009363:Neoplasm Proteins; D010320:Parvalbumins; C034733:oncomodulin; C017173:dansylaziridine; D003545:Cysteine; D002118:Calcium