Bilirubin and haeme binding to human serum albumin studied by spectroscopy methods

Cobinding of bilirubin and of haeme to human serum albumin was investigated by means of difference absorption spectroscopy and fluorescence spectroscopy. Two specific sites for bilirubin and two for haeme binding occur on the albumin molecule. The primary binding site for bilirubin (Ka = 2.5 microM-1) is different from the primary heame binding site (Ka = 50 microM-1; Beaven et al., Eur J. Biochem. 41, 539-546, 1974), the former, however, might be identical with the secondary center for haeme binding. Similarly, the primary haeme binding center might be identical with the secondary bilirubin binding site.