Macromolecular crowding affects protein photosensitivity: The case of egg white immunoreactivity

An aqueous solution containing 0.1 g/l egg white proteins was exposed to increasing irradiance (0, 1.6, 7.2, 10.5, 17.0 and 29.1 W m−2) UV-C light for up to 30 min at 8 °C. In all cases, a decrease in immunoreactivity was detected. A 10-fold decrease of immunoreactivity was obtained in circa 7 min at 29.1 W/m2 and in more than 4 h at 1.6 W/m2. The loss of immunoreactivity was attributed to denaturation phenomena leading to the formation of protein fragments partially retaining the original epitopes. A progressive decrease in protein photosensitivity was observed by increasing its concentration. Above a limit concentration of 2.2 g/l, egg white proteins became extremely resistant to UV-light, even prolonging exposure time at 29.1 W/m2 to 3 h. Photostability of egg white proteins was attributed to the occurrence of crowding effects which favoured protein folding and hindered photolysis.