Multiple forms of soluble invertases in sugarcane juice: Kinetic and thermodynamic analysis
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Soluble invertases were partially purified from storage tissue of an early maturing and high sucrose accumulating genotype Co89003 using ammonium sulphate fractionation and DEAE-cellulose column chromatography. The three different acid invertase isoforms named as A-I, A-II and A-III were identified at late grand growth stage of cane development, whereas only one neutral invertase isoform was detected at maturity stage of cane growth. The final purification achieved for A-I, A-II, A-III and neutral invertase isoform was 37, 45, 7 and 17-fold, respectively. The optimum pH values for A-I, A-II, A-III and neutral isoform were observed to be 5.0, 4.5, 4.5 and 7.0, respectively. Apparent Michaelis constant i.e. Km of different acidic isoforms at its optimum pH and temperature varied from 50.0 to 83.3 mM. For neutral invertase isoform, Km value was 44.0mM at its optimum pH and temperature. The highest Vmax/Km value of A-I isoform indicates the maximum kinetic perfection of this isoform and it may be the major vacuolar enzyme involved in sucrose hydrolysis. From the study of effect of temperature on Km and Vmax values of neutral invertase isoform, the enthalpy change, entropy change and energy of activation were observed to be -21.1 kJ mol-1,-40.5 JK-1 mol-1, and 42.5 kJmol-1, respectively. Among the different metal ions tested, manganese chloride strongly inhibited the activity of all soluble acid invertase isoforms and thus, may be utilized to induce early maturity and controlling sucrose inversion in sugarcane thereby increasing sugar recovery.
Key WordsSugarcane Sucrose Storage Invertase Isoforms Kinetics Invertase inhibitors
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