UV-Light Exposure of Insulin: Pharmaceutical Implications upon Covalent Insulin Dityrosine Dimerization and Disulphide Bond Photolysis
Figure 4
Fluorescence emission of human insulin (276 nm excitation) upon prolonged 276 nm UV-excitation.
(A) Fluorescence emission spectra (276 nm exc.) obtained before and after 276 nm light continuous exc. (0.5 h, 1 h, 1.5 h, 2.5 h, 3.5 h, and 7 h) of human insulin in solution. There is a continuous decrease in emission intensity at 303 nm with 276 nm exc. time. The insert shows a zoom of the emission spectra between 350 and 550 nm. Emission intensity at ∼405 nm increases progressively with 276 nm excitation time. (B) Fluorescence emission intensity kinetic traces obtained at 330 and 405 nm (exc. fixed at 276 nm) upon continuous of human insulin with 276 nm light. Fitting of the experimental traces was carried out using an exponential function F(t) = C1– C2.e−kt. Fitted parameter values and corresponding errors, and root mean square error values were obtained after fitting each kinetic trace (Table 2).