Bioluminescence of coelenterates: spectral components

Ca2+-regulated photoproteins are responsible for the bioluminescence of marine coelenterates. The addition of calcium ions to Ce-regulated photoproteins results in light emission. This peculiar feature of the photoproteins provides the basis for their analytical application, mainly in monitoring intracellular calcium concentration. During the study, the complex bioluminescence spectra of photoproteins from marine coelenterates, e.g. the jellyfish Aequorea victoria and the hydroid Obelia longissima, and photoluminescence spectra of products of the bioluminescent reactions (Ce-discharged photoproteins) were resolved into spectral components. Resolution of the spectra was performed in a combined way, involving methods of: (a) function increment based on Gaussian distribution; (b) secondary derivatives; and (c) optimization of spectral components' parameters and minimization of divergence. The spectral components were attributed to four forms of coelenteramide - unionized and three ionized forms. The bioluminescence spectra were found to include all the four forms of coelenteramide, but the photoluminescence spectra included only two: the Ce-discharged obelin produces fluorescence of two ionized forms, and the discharged aequorin both unionized and ionized forms. The differences in bioluminescence and photoluminescence spectra of the discharged photoproteins are explained by the different protonic environments of coelenteramide in these proteins.