Interaction Between Drugs and Water-Soluble Polymers. VII. Binding of Berberine with Bovine Serum Albumin

The interaction between berberine chloride (BC) and bovine serum albumin (BSA) was studied by equilibrium dialysis. Since the number (n) of binding sites per mole of BSA was large, the binding was nonspecific. Then the binding capacity (nK) was evaluated instead of the binding constant (K). According to the dependence of the NK value on ionic strength, the interaction was due to hydrophilic binding. Intermolecular interaction of BC was observed by the concentration (1–10 mmol/L) dependence of 1H-NMR parameters; that is, the respective signals shifted to a higher magnetic field, the spin-lattice relaxation time (T 1) decreased, and the spin-spin relaxation rate (T 2 −1) increased. The interaction of BC with BSA (1.45 × 10−4 mol/L) resulted in a decrease in T 1, an increase in T 2 −1, and little variation of the chemical shift. On the basis of the ratio of the spin-spin relaxation rate of bound BC to free BC (T 2b −1/T 2f −1). the binding position of BC to BSA was considered to be spread over the entire BC molecule because of the rigid ring structure of BC even if the binding was nonspecific and hydrophilic.