The temperature dependence of the fluorescence decay of low-density lipoproteins

The decay of the intrinsic tryptophan fluorescence of low-density lipoproteins (LDL) is measured using a picosecond laser system with an excitation wavelength of 295 nm. The emission wavelengths were observed at 320, 340 and 360 nm. The measurements were performed in the temperature range 10-45 degrees C. The fluorescence decay data are analysed in terms of: (i) three exponentials; (ii) a continuous distribution of exponentials; and (iii) the average decay time. The results indicate that the tryptophans are in a non-polar environment and that the fluorescence is not affected by phase transitions found to occur in the lipid core of the LDL molecule.