Biochemical relationship of phosphoenolpyruvate carboxylases (PEPCs) from thermophilic archaea

An archaeal phosphoenolpyruvate carboxylase (PEPC) was purified from an acidophilic extreme thermophile, Sulfolobus acidocaldarius. The native enzyme was a homotetramer of 260±20 kDa molecular mass composed of 60±5 kDa subunits. The enzyme appeared to have a temperature optimum of 90°C and a pH optimum of 8.0. The activity of S. acidocaldarius phosphoenolpyruvate carboxylase was inhibited by l-aspartate and l-malate, but not enhanced by any metabolites. In comparison to the enzymatic and molecular properties of all other phosphoenolpyruvate carboxylases including another archaeal entity from the hyperthermophilic methanogen Methanothermus sociabilis, the archaeal phosphoenolpyruvate carboxylases were quite different from bacterial and eucaryal counterparts, and their small size and the lack of positively allosteric regulation were likely to be peculiar to the enzyme of the domain Archaea.