Binding Parameters of Theophylline and Aminophylline to Bovine Serum Albumin

Abstract

The interaction of theophylline and bovine serum albumin (BSA) was investigated by using the equilibrium dialysis method. The experiments were carried out at 5°C and at pH 6.85 using 1/15 M phosphate buffer. The binding parameters determined are as follows ; n₁=0.48, n₂=1.34, K₁=2.89×10³ M^-1, and K₂=4.03×10²M^-1. The interaction of aminophylline with BSA was also investigated in the same manner. The binding parameters are as follows ; n₁=0.43, n₂=1.29, K₁=2.74×10³M^-1, and K₂=5.61×10²M^-1. These parameters are calculated on the basis of theophylline content in aminophylline, which is a 2 : 1 complex of theophylline with ethylenediamine. There was little difference in binding parameters between theophylline and aminophylline. This is to be expected in view of the findings that under the experimental conditions used, theophylline does not interact significantly with ethylenediamine, and the latter shows essentially no interaction with BSA.