[Examination of the protein binding of lidocaine by gel filtration method].

The protein binding of lidocaine has been studied using gel filtration method. Thermodynamic calculation has been done on results of the experiment. We have found that the primary bond type of lidocaine with serum albumin is hydrophobic interaction, because entropy (delta S) is constantly positive (> 0) under these experimental conditions. The change of the binding ratio between lidocaine and serum albumin with changing pH results from the conformational change of the serum albumin, but the protein binding of lidocaine is also an exothermic reaction. The following conclusions have been obtained. (1) The binding of serum albumin with lidocaine is nonspecific and mainly the result of hydrophobic interaction. (2) At temperature 35 degrees C and pH 7.5, binding constant (K) and binding site (np) of bovine serum albumin with lidocaine are K = 5.9 x 10(3) M-1 and np = 103.5 x 10(-6) M, respectively. (3) Increasing binding ratio with increase in pH is the result of the increase in binding site. This involves the conformational change of albumin, especially that of N-B transition. (4) The binding of serum albumin with lidocaine is an exothermic reaction. Therefore, the binding of lidocaine with serum albumin increases as the temperature decreases.