Thermal and Photochemical Effects on the Fluorescence Properties of Type I Calf Skin Collagen Solutions at Physiological pH

Abstract

Mammalian collagens exhibit weak intrinsic UV fluorescence that depends on the age and previous history of the sample. Post-translational modifications result in additional fluorescent products (e.g. DOPA, dityrosine, and advanced glycation end products (AGE)). UV radiation can cause longer wavelength fluorescent oxidative bands. These alterations can assess the extent of photolysis. We describe the ground-and excited-state oxidative transformations of newly-purchased type I calf skin collagens (samples #092014 and #072012) and a 7-year-old sample (#072005). We compare the effects of UV radiation (mainly 254 nm) and age on the photochemical reaction kinetics and fluorescence spectral distribution of type I calf skin collagen at pH 7.4. The fluorescence spectra of samples #072012 and #092014 were similar but not identical to pure tyrosine, whereas #072005 indicated significant "dark" oxidation at the expense of tyrosine. Fading of oxidized product(s) at 270/360 nm is second-order. Build-up of 325/400 nm (dityrosine) fluorescence is linear with time. Rate parameters r2 and r 1 were respectively proportional to second order disappearance of ground state oxidation products and the quasi-first-order photochemical formation of dityrosine. There is a reciprocal relationship between the rates of decrease in the 270/360 nm fluorescence and concomitant increase in 325/400 nm fluorescence. Their relative rates depend on the age of the collagen sample. There is a reciprocal relationship between r 1 and r 2 . This relationship results because both ground state autoxidation and excited state photo-dimerization proceed via a common tyrosyl radical intermediate. Water of hydration appears to play a role in generating tyrosyl radical.

The Interaction(s) between Calf-Skin Hyaluronic Acid (Hyaluronan) and Dermal Type I Calf-Skin Collagen under 254 nm UV Radiation: Ability of Hyaluronan to Alter Qualitative and Quantitative Dimerization of Collagen Tyrosine Residues

“…Our work demonstrates that collagen-bound tyrosine qualitatively behaves similarly to Shimazu's system in unbound tyrosine [10] [11] at physiological pH. Interactions between collagen and surrounding ECM could either facilitate or retard dimerization which results in the temperature-dependent shifts in R ratios, seen in Figure 2 and Figure 3.…”

The Relationship between the Strength Characteristics of Cerebral Aneurysm Walls with Their Status and Laser-Induced Fluorescence Data

“…Its longer wavelength side differs from sample to sample, sometimes forming local maxima around 450 and 550 nm. It could also appear due to the crosslinks in collagen [ 15 , 16 ].…”

“…As it was mentioned above, this is possible for all these fluorophores are not excited independently but form a structure in which absorbed energy is distributed between fluorophores. Studies performed at longer excitation wavelengths [ 15 , 16 , 22 , 23 ] show that various molecular groups in collagen could fluoresce in the observed bands. Spectral features are species-specific and strongly depend on the type of tissue from which collagen was taken.…”