Protein fluorescence and its relationship to free radical activity.

Evidence for free radical involvement in pathological processes is often indirect and frequently depends upon the detection of characteristic changes in tissue constituents, particularly polyunsaturated lipids. Free radical attack on protein leads to specific oxidative changes in their constituent amino acids, principally cysteine, tryptophan and tyrosine. This is associated with the induction of characteristic fluorescence (excitation 360 nm, emission 454 nm) and protein aggregation. This observation leads to a suitable assay for studying protein oxidation, and such fluorescent proteins may be relevant in the pathogenesis of diabetic microangiopathy and rheumatoid arthritis.