Phosphoenolpyruvate carboxylase (PEPC) was purified for the first time from hyperthermophilic archaeon Methanothermus sociabilis, growing autotrophically with an optimum at 88°C. The optimum temperature for enzyme activity was similar to that for growth and was 85°C. The native enzyme was a homotetramer of 240 kDa molecular mass and the subunit displayed an apparent molecular mass of 60 kDa. The archaeal PEPC was insensitive to various metabolites which are known as allosteric effectors for most bacterial and eucaryal counterparts. The enzyme showed extreme thermostability such that there remained 80% of the enzyme activity after incubation for 2 h at 80°C. These results implied that archaeal PEPC was significantly different from bacterial and eucaryal entities.
