Enhanced protein degradation by photoilluminated riboflavin in the presence of Cu(II).

Riboflavin is known to generate superoxide anion upon photoillumination and in the presence of Cu(II) causes fragmentation of DNA. In the present study we examined the effect of riboflavin and Cu(II) on bovine serum albumin, invertase and lysozyme. Using fluorescence quenching experiments, it is shown that riboflavin binds to protein and causes fragmentation which in the presence of Cu(II) is enhanced. Using neocuproine as the Cu(I) sequestering reagent, it has also been shown that Cu(I) is an essential intermediate in the protein fragmentation reaction. Results obtained with various scavengers of active oxygen species strongly suggest that the species predominantly responsible for protein breakage is hydroxyl radical.