PROCESS OF THERMAL-DENATURATION OF XYLANASE (XYNB) FROM CLOSTRIDIUM-STERCORARIUM F9

The thermal denaturation process of Clostridium stercorarium F-9 xylan ase (XynB) was studied by monitoring remaining activity and recovered activity of the enzyme. At pH 5.5, aggregation occurred rapidly after the thermal denaturation initiated. The aggregated protein could be di ssolved in 8 M urea solution, and the enzyme activity was recovered by diluting the urea. The extent of the recovered activity was gradually decreased with two phases as the reaction time of the thermal denatur ation became longer. These results suggested the thermal denaturation process to be as follows: [GRAPHICS] where N is the native state of th e enzyme; D1 is the denatured state of the enzyme that is formed rapid ly after the reaction started and can be renatured by the urea treatme nt, and D2 and D3 are the denatured states of the enzyme that cannot b e renatured even by the urea treatment. The rate constants were k(1) > 9.2, k(2) = 0.33, and k(2) = 0.57, and k(3) = 0.13 (in min(-1) unit).