Cellulase obtained from Bacillus subtilis ITBCCB148 has successfully been isolated and purified. The native enzyme was modified with dimethyladipimidate (DMA) to increase the stability of the enzyme. The native and modified enzymes were characterized including determination of optimum temperature, optimum pH and thermal stability. The activity of the cellulase was determined based on Mendels method and the protein content was determined based on Lowry method. The results showed that the native enzyme has optimum temperature of 55 o C and optimum pH of 5.5. The thermal stability for 60 minutes at temperature of 55 o C indicated that the native enzyme has k i = 0.034 min.t -1 , t 1/2 = 20.4 min., and Δ Δ Δ Δ ΔG i = 100.9 kJ/mol. The modified enzyme with modification degrees of 64.5; 69.5 and 82% have optimum temperature of 55 o C and optimum pH of 6. The thermal stability for 60 minutes at temperature of 55 o C of the modified enzyme with modification degrees of 64.5; 69.5 and 82% have k i values of 0.024; 0.021 and 0.022 min. -1 , t 1/2 values of 28.9; 33.0 and 31.5 minutes, and Δ Δ Δ Δ ΔG i values of 101.9; 102.3 and 102.2 kJ/ mol, respectively. The modification with DMA has successfully increased the thermal stability of the modified enzymes between 1.4 -1.6 times compared to that of the native enzyme. The decrease of ki values, increase of half-lives and Δ Δ Δ Δ ΔG i indicated that the modified enzymes were more stable compared to the native enzyme.

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 55 o C and 6, respectively. The thermal stability test of native enzyme for 60 min. at temperature of 55 o C gave values of thermal inactivation rate constant (k i ) 0.035/min., half-life (t 1/2 ) 19.80 min. and denaturation energy ΔG i )= 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 k i values were 0.014; 0.012 and 0.011, respectively. Their t 1/2 values were 49.5; 57.75 and 63 min., respectively; and their ΔG i 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