Kinetic Studies of Aspartase from Hafnia alvei by Temperature Dependence Activity Changes

摘要

The temperature dependence of the kinetic parameters of the aspartase-catalyzed reaction has been examined in the direction of deamination. The pK1values at 37 o C, 25 o C, 16 o C and 7 o C were 6.2 【 0.1, 6.3 【 0.1, 6.7【0.3 and 6.9 【 0.3, respectively. On the other hand, the pK2 values at 37 o C,25 o C, 16 o C and 7 o C were 8.1 【0.2, 8.3 【 0.2, 8.2 【 0.3 and 8.0 【 0.2,respectively. The enthalpy of ionization, DHion, calculated from the slope of pK1, are 6.0 【 0.3 kcal/mol. These results validate the prediction that aspartase requires a histidine residue for a general base, and a cysteine (or having a carboxyl functional group) for a general acid.