Influence of divalent cations on the structural thermostability and thermal inactivation kinetics of class II xylose isomerases.

摘要: The effects of divalent metal cations on structural thermostability and the inactivation kinetics homologous class II d-xylose isomerases (XI; EC 5.3.1.5) from mesophilic (Escherichia coli Bacillus licheniformis), thermophilic (Thermoanaerobacterium thermosulfurigenes), hyperthermophilic (Thermotoga neapolitana) bacteria were examined. Unlike three less XIs that substantially structurally stabilized in presence Co2+ or Mn2+ (and Mg2+ to a lesser extent), melting temperature [(Tm) approximately 100 degrees C] T. neapolitana XI (TNXI) varied little absence single type metal. In any two these metals, TNXI exhibited second transition between 110 C 114 C. kinetic inactivation, which was non-first order, could be modeled as two-step sequential process. 5 mm at 99-100 slowest Mn2+[half-life (t(1/2)) 84 min], compared (t(1/2) 14 min) 2 min). While adding increased TNXI's t(1/2) 7.5 min, showed no significant activity temperatures above first transition. results reported here suggest that, unlike other examined, metals are required for activity, but not essential its thermostability. form corresponding is known, likely cooperative interactions dissimilar binding sites.