Modulation in the photosensitivity of albumin-bound bilirubin.

Exposure of BR-albumin complexes to visible light at pH 8.0 led to a change in the fluorescence intensity at 525 nm, which was found to be different for different serum albumins. Whereas a complex of BR with human serum albumin (HSA) showed a marked increase in fluorescence upon photoirradiation, BR-sheep serum albumin (SSA) complex failed to produce a marked increase. On the other hand, a complex of pig serum albumin (PSA) with BR produced a remarkable decrease in fluorescence upon photoirradiation. Equilibration of these complexes with approximately 20 mM chloroform for 1 h resulted in alteration in the photoinduced fluorescence. These photoinduced fluorescence modulations were found to be concentration dependent. Photoirradiation of BR-HSA complex led to a significant decrease in the positive CDCEs of the bisignate CD spectra in a time dependent manner that can be reconciled, to a significant extent, in the presence of chloroform. Taken together, all these results suggest that chiroptical properties/stability of albumin-bound BR varies with albumin species, protein concentration and the presence of chloroform.