Fluorescence of putative chromophores in Skh-1 and citrate-soluble calf skin collagens.

Background/purpose: Fluorescence of Skh-1 hairless mouse and calf skin acid-soluble type I collagens are envelopes of several bands putatively due to tyrosine (excitation/emission peak at 275/300 nm), dihydroxyphenylalanine (dopa; 280/325 nm), tyrosine aggregate (285/360 nm), dityrosine 325/400 nm), and advanced glycation end (AGE) product (370/450 nm), respectively. As these fluorophores can be markers of pathological conditions, we wish to present further evidence for or against these assignments.

Methods: We analysed intact type I mouse collagens and AGE by conventional fluorescence spectroscopy, synchronous spectroscopy, high-performance liquid chromatography (HPLC), and borate quenching.

Results: The relative amount of each fluorophore depends on the collagen sample. Acid- or enzyme-hydrolysis results in loss of fluorescence intensity at 350-400 nm, and enhanced emission 400-500 nm which could be reproduced by controlled dopa oxidation. Borate buffer quenches fluorescence at lambda>400 nm from intact collagens, dityrosine, dopa, and oxidized dopa but does not quench tyrosine or AGE fluorescence.

Conclusion: Collagen fluorescence depends on its source and previous history. The data indicate that collagen fluorescence is derived from tyrosine, dopa, interacting tyrosine residues, covalent dityrosine, and dopa oxidation product(s), but not AGE.