Enzymatic and structural characterization of type II isopentenyl diphosphate isomerase from hyperthermophilic archaeon Thermococcus kodakaraensis

Enzymatic and thermiodynamic characteristics of type It isopentenyl diphosphate (IPP):dimethylallyl diphosphate (DMAPP) isomerase (Tk-IDI) from Thermococcus kodakaraensis, which catalyzes the interconversion of IPP and DMAPP, were examined. FMN was tightly bound to TA-IDI, and the enzyme required NADPH and Mg-m(m)p(2+ for the isomerization in both directions. The melting temperature (T)), the change of enthalpy (DH(), and the heat capacity change (DC)) of Tk-IDI were 88.0C, 444 kJ mol-1, and 13.2 kJ mol-1 K-1, respectively, indicating that Tk-IDI is fairly thermostable. Kinetic parameters dramatically changed when the temperature crossed 80C even though its native overall structure was stably maintained up to 90C, suggesting that local conformational change would occur around 80C. This speculation was supported by the result of the circular dichroism analysis that showed the shift of the a-helical content occurred at 80C. 2005 Elsevier Inc. All rights reserved.