Cultivar variation in heat stability and kinetic properties of soluble invertase in wheat grains

Soluble invertase from mid-milky stage grains of two wheat (Triticum aestivum L.) varieties, namely Kalyansona and PBW 343 was isolated and purified by employing ammonium sulphate precipitation, gel filtration on Sephadex G-150 and DEAE-cellulose column chromatography. Invertase from Kalyansona exhibited greater heat stability (50 °C) compared to PBW 343 (35 °C). By employing photo-oxidation and chemical modification methods, and by studying the effect of pH on Km and Vmax, the involvement of histidine, sulphydryl and α-carboxyl groups in the active site of the enzyme was indicated. The enzyme was completely inhibited by HgCl₂ and DTNB. ZnSO₄, MgSO₄, KCl, CaCl₂, EDTA and pyridoxine were strong inhibitors in PBW 343 but not in Kalyansona. The two varieties also showed differential response in respect to thermodynamic properties of the enzyme, i.e. energy of activation (Ea), enthalpy change (ΔH) and entropy change (ΔS). Overall the results suggest that genetic differences exist in soluble invertase properties of wheat grains and that the thermal adaptation of the enzyme is reflected in its altered kinetic behaviour.