Theoretically obtained insight into the effect of basic amino acids on Cypridina bioluminescence

Because of high bioluminescent quantum yields, independent cofactors, high signal-to-noise ratio, Cypridina bioluminescence has been successfully applied to gene reporter assays, enzyme immunoassays, immunohistology and imaging. Although the chemical reaction that transforms Cypridina luciferin into Cypridina oxyluciferin is clearly defined, the environmental effects on the spectrochemistry of Cypridina oxyluciferin continue to be a particularly intriguing aspect. In this paper, the solvent effect on the fluorescent spectrum, the basicity of amino acids and the degree of covalent character of hydrogen bond were studied by a theoretical Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT) approach. Our results demonstrate that the emission wavelengths varied little with solvent polarity. The compositive effects of basic amino acid and polarity of the environment only slightly affected the structure and spectroscopic properties. The fluorescent properties of Cypridina oxyluciferin can be modulated by the covalent character of the hydrogen bond.