Binding (in vitro) of some antimitotic isatin derivatives to human serum albumin

The binding of isatin and its mustard N-Mannich base, considerably biologically active compounds, to human serum albumin has been studied by equilibrium dialysis and ultrafiltration. The influences of ligand and macromolecule concentration, temperature and pH of the incubation medium have been demonstrated. The Scatchard plot of isatin binding to albumin shows a biphasic curve which indicates the presence of at least two different binding sites on albumin molecule. One site with a higher affinity, K1 = 2.25 X 10(3) M and n1= 25, and the other site with a lower affinity, i.e. higher capacity. In the cases of mustard Mannich base we could demonstrate the same type of curve, K1 = 2.20 X 10(5) M and n1 = 1.0, whereas another site has a lower affinity and greater number of binding sites.