الوصف:
<p>The research aims to study the effect of chemical modification on the stability of protease enzyme from a local bacteria isolate <em>B</em><em>.</em><em> subtilis</em> ITBCCB148 with NPC-PEG. The result showed that the native enzyme has optimum pH and temperature of 6.5 and 60°C, respectively. The stability test of the native protease at pH 6.5 and temperature 60°C for 360 minutes produce the following results: the residual activity of 5.75%, t½= 84.5 min., k<sub>i</sub> = 0.0082 min.<sup>-1</sup>, and ?G<sub>i</sub> = 106.508 kJ mol<sup>-1</sup>. The modified enzyme with NPC-PEG (33%, 42%, and 75%), showed that the optimum pH did not changed, however, the optimum temperature shifted from 60°C to 65°C. The stability tests of the modified enzyme with NPC-PEG have increased of 2.06; 2.24; and 2.31 times, respectively, than that of the native one. The decrease of ki, the increase of t½ and ?G<sub>i</sub> of the modified enzymes with NPC-PEG demonstrated that upon modification, the enzyme became more stable. This might due to rigidity increase of the modified enzyme, so the active structure of the enzyme is maintained and is protected from unfolding process.</p>