ADSORPTION BEHAVIOR OF INSULIN AND SOYBEAN TRYPSIN-INHIBITOR AT THE MERCURY SOLUTION INTERFACE/

The adsorption of insulin and soybean trypsin inhibitor (STI) on the m ercury electrode was investigated with phase-sensitive alternating cur rent (ac) polarography. The investigations focused on the effect of in sulin and STI concentrations on the capacitive ac component over a wid e potential range at pH 8.8, when both proteins are in folded form, an d at pH 1.0 when they are unfolded. Besides a pseudo-capacitance due t o the faradaic process of protein -S-S- bond reduction, the presence o f protein adsorption of the Frumkin type was established. From the ana lysis of the corresponding adsorption isotherms, the relevant thermody namic adsorption parameters were determined. Similarities in the adsor ption characteristics of both proteins studied were demonstrated, and the differences in the adsorption behaviour between native and denatur ed proteins were proven. The data obtained is also discussed from the aspect of protein disulphide bond interaction with mercury. (C) 1998 E lsevier Science S.A. All rights reserved.