Binding of hypocrellin B to human serum albumin and photo-induced interactions

Molecular binding of hypocrellins to human serum albumin (HSA) needs to be further clarified considering the phototherapeutic potentials of hypocrellins to vascular diseases. In the current work, it was estimated that the binding constant of hypocrellin B (HB) to HSA was 2.28 x 10(4) M(-1). Furthermore, based on the fluorescence responses for both HB and the tryptophan of HSA, it was suggested that the binding of HB to HSA should be more specific rather than distributed randomly on the surface of HSA, which was also confirmed by photobleaching of the tryptophan via photosensitization of HB. Besides, it was found that both of the photo-bleaching of the tryptophan and the photo-oxidation of HB were principally oxygen-dependent, suggesting reactive oxygen species generated via the photosensitization of HB, instead of the free radicals of the photosensitizer (HB*-), play the most important role in photodynamic processes.