1. Institute of Biochemical Physics, Russian Academy of Sciences, Vavilov St. 28, 119991 Moscow, Russia;2. Laboratoire d'Etude des Interactions des Molécules Alimentaires, Institut National de la Recherche Agronomique, B.P. 71627, 44316 Nantes Cedex 03, France;3. Nestec Research Centre, Vers-chez-les-Blanc, P.O. Box 44, CH 1000, Lausanne, Switzerland
Abstract:
Thermal denaturation and renaturation of soybean trypsin (Kunitz) inhibitor (STI) were studied by high-sensitivity differential scanning calorimetry in the presence of polysaccharides (dextran, ι- and κ-carrageenans, gum arabic, pectins and dextran sulfate). This study was carried out under conditions of both thermodynamic incompatibility and complex formation of STI and polysaccharides. The presence of polysaccharides did neither influence the denaturation temperature nor the denaturation enthalpy of STI under conditions of their incompatibility with the protein. No polysaccharide (except gum arabic) affected the ability of STI to renature and recover its inhibitory activity after thermal denaturation. At acidic pH values, the protein was shown to form electrostatic complexes with pectins and dextran sulfate. Substantial destabilisation of STI bound to dextran sulfate was observed. In the case of STI/pectin complexes, either a decrease or increase in the stability of STI was observed depending on the complex composition and esterification degree of pectin. The mechanism behind the changes in stability of STI bound to the polysaccharide matrix is discussed. Thermal denaturation of STI in complexes with dextran sulfate and pectin was completely irreversible. This observation indicates a possibility of suppressing antinutritional activities of trypsin inhibitors in soy products.
Schematic presentation of the denaturation of a protein (P) bound to a polymer matrix (M): (A) loose protein occupancy, (B) dense protein occupancy.
