Spin and fluorescence label studies on bile salt micelles

The interior structure of micelles formed by bile salts, which differ in the number and location of the hydroxyl groups attached to the steroid nucleus, was studied by the spin label and fluorescence label methods. The results show that the interior structure of micelles formed by bile salts possessing two hydroxyl groups is more rigid than that of micelles formed by trihydroxy bile salts regardless of the terminal hydrophilic group. Even in the case of dihydroxy bile salts possessing two hydroxyl groups in the same location, the interior structures of their micelles are different from each other depending on the orientation of their hydroxyl groups. It is considered that hydroxyl groups as well as the terminal hydrophilic group play an important role in the micellar formation of bile salts.