Binding Characteristics of Tryptophan Metabolites to Bovine Serum Albumin

The interaction betwen tryptamine, 3-indoleacetic acid and 5-hydroxyindole-3-acetic acid and bovine serum albumin (BSA) was investigated using the equilibrium dialysis technique. The apparent binding constant was determined assuming the equivalence and independence of the binding sites on the BSA molecule. The binding constants of tryptamine, 3-indoleacetic acid and 5-hydroxyindole-3-acetic acid with a single binding site are 1.07 (0.14)×10^4M^<-1>, 1.73 (0.15)×10^4M^<-1> and 2.02 (0.15)×10^4M^<-1> at 25℃ at pH 6.5,respectively. The affinity of the tryptophan metabolites to BSA strengthened with progression of the metabolic process, and it reached a maximum at a relatively narrow pH region of 6 to 8.