Increasing stability of cellulase, obtained from Bacillus subtilis ITBCCB148 with chemical modification using p-nitrophenolcarbonate-polyethylenglycol (NPC-PEG)

Abstract

This research aims to increase the stabilty of cellulase obtained from local bacteria isolate Bacillus subtilis ITBCCB148 by chemical modification using p-nitrophenolcarbonate polyethylenglycol (NPC-PEG). The characterization of the native and modified enzymes were performed by determination of optimum pH and temperature as well as thermal stability. The result showed that the native enzyme has optimum temperature and pH is 55oC and 6, respectively. The thermal stability test of native enzyme for 60 min. at temperature of 55 oC gave values of thermal inactivation rate constant (ki) 0.035/min., half-life (t1/2) 19.80 min. and denaturation energy ΔGi)= 100.908 kJ/mol. The modified enzymes with modification degree of 63, 70 and 81% have the same values of optimum temperature and pH as native enzyme, but their stability data have increased very significantly. Their ki values were 0.014; 0.012 and 0.011, respectively. Their t1/2 values were 49.5; 57.75 and 63 min., respectively; and their ΔGi values were 103.407; 103.828 and 104.065 kJ/ mole, respectively. Thus, the chemical modification using NPC-PEG has shown to increase the enzyme stability of modified enzyme 2.5 – 3.2 times compared to the native enzyme, although no change of optimum temperature and pH was observed.