Temperature dependence of photochemical fluorescence fading in Skh-1 hairless mouse collagen

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. Collagen solutions were exposed to radiation from 0 to 240 min from either a UVG-11 hand lamp, total dose=1.173 x 10(3) J/m(2); a UVL-21 hand lamp total dose=2.030 x 10(3) J/m(2); or the fluorometer, at 325 +/- 5 nm, total dose=0.156 x 10(3) J/m(2). 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 degrees C. 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 E-a similar to 0 and coil E-a=7.6 +/- 0.6 kcal/mol (31.7 +/- 2.5 kJ/mol). 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.