Monitoring and kinetic parameter estimation for the binding process of berberine hydrochloride to bovine serum albumin with piezoelectric quartz crystal impedance analysis

A new method for monitoring, in real time, the drugbinding process to protein with piezoelectric quartz crystal impedance (PQCI) is proposed. The method was used to monitor the binding process of berberine hydrochloride to bovine serum albumin (BSA). BSA was immobilized on the silver electrode surface of a piezoelectric quartz crystal and the optimized experimental conditions were established. The BSA-coated piezoelectric sensor was in contact with berberine solution. The time courses of the resonant frequency and equivalent circuit parameters of the sensor during the protein-drug binding were simultaneously obtained. On the basis of the analysis of the multidimensional information provided by PQCI, it was concluded that the observed frequency decrease was mainly ascribed to the mass increase of the sensor surface resulting from the binding. According to the frequency decrease with time, the kinetics of the binding process were quantitatively studied. A piezoelectric response model for the binding was theoretically derived. Fitting the experimental data to the model, the kinetic parameters, such as the binding and dissociation rate constants (k(1) and k(-1)) and the binding equilibrium constant (K.), were determined. The k(1), k(-1), and K-a values obtained at 25degreesC were 67.5 (+/-0.1) (mol liter(-1))(-1) s(-1), 1.7 (+/-0.1) X 10(-3) s(-1), and 3.97 (+/-0.06) X 10(4) (mol liter(-1))(-1), respectively. (C) 2002 Elsevier Science (USA).