Type I mammalian collagens have several photolabile fluorescent moieties that absorb UV rays capable of reaching the dermis. We studied the temperature dependence of fluorescence fading as a marker of photochemical damage.Methods:
Collagen solutions were exposed to radiation from 0 to 240 min from either a UVG-11 hand lamp, total dose=1.173 × 103 J/m2; a UVL-21 hand lamp total dose=2.030 × 103 J/m2; or the fluorometer, at 325±5 nm, total dose=0.156 × 103 J/m2. We recorded intensities at excitation/emission wavelengths 270/300, 270/330, 270/360, 270/400, 325/400, and 370/450 nm at T=9.0–59.3 °C.Results:
Results indicated simultaneous forward and reverse reactions. However, the 270/360 nm fluorophore could be analyzed as a second-order reaction. The Arrhenius curve showed two straight lines intersecting near the denaturation temperature, with helix activation energy Ea∼0 and coil Ea=7.6±0.6 kcal/mol (31.7±2.5 kJ/mol).Discussion:
Collagen-bound fluorophores are not just passive markers of oxidative stress and age-related damage. Their photolability to wavelengths reaching the dermis may result in pathological conditions, particularly at elevated body temperatures.