Purification and biochemical characterization of insoluble acid invertase (INAC-INV) from pea seedlings

Invertase (EC 3.2.1.26) catalyzes the hydrolysis of sucrose into d-glucose and d-fructose. Insoluble acid invertase (INAC-INV) was purified from pea (Pisum sativum L.) by sequential procedures entailing ammonium sulfate precipitation, ion exchange chromatography, absorption chromatography, reactive green-19 affinity chromatography, and gel filtration. The purified INAC-INV had a pH optimum of 4.0 and a temperature optimum of 45 °C. The effects of various concentrations of Tris-HCl, HgCl ₂, and CuSO ₄ on the activities of the purified invertase were examined. INAC-INV was not affected by Tris-HCl and HgCl ₂. INAC-INV activity was inhibited by 6.2 mM CuSO ₄ up to 50%. The enzymes display typical hyperbolic saturation kinetics for sucrose hydrolysis. The K _m and V _max values of INAC-INV were determined to be 4.41 mM and 8.41 U (mg protein) ^-1 min ^-1, respectively. INAC-INV is a true member of the β-fructofuranosidases, which can react with sucrose and raffinose as substrates. SDS-PAGE and immunoblotting were used to determine the molecular mass of INAC-INV to be 69 kDa. The isoelectric point of INAC-INV was estimated to be about pH 8.0. Taken together, INAC-INV is a pea seedling invertase with a stable and optimum activity at lower acid pH and at higher temperature than other invertases.