The phosphoenolpyruvate synthase (EC 2.7.9.2) from the hyperthermophilic archaeon Pyro coccus furiosus catalyzes the Pi-dependent formation of pyruvate, ATP and water from phosphoenolpyruvate and AMP [Sakuraba, H. et al., Arch. Biochem. Biophys., 364, 125-128 (1999)]. In this study, the P furiosus phosphoenolpyruvate synthase was purified to homogeneity and the N-terminal amino acid sequence was determined to be AYRFIKWFEELS. The sequence coincided completely with the N-terminal amino acid sequence of the translation product of the mIrA gene that was found to be upregulated at the transcriptional level by the (x-linked glucose disaccharide maltose [Robinson, K. A. and Schreier, H. J., Gene, 151, 173-176 (1994)]. The MlrA gene was cloned and expressed in Escherichia coli. The recombinant cells produced a hyperthermostable phosphoenolpyruvate synthase. This indicates that the mlrA gene encodes the enzyme. When P furiosus was grown on the medium supplemented with maltose, the specific activity of the enzyme markedly increased (about 10-fold) compared with that produced by the cells grown on the medium without maltose. Northern blot analysis revealed enhanced transcription of the mlrA gene in the presence of maltose. These results indicate that transcriptional regulation of phosphoenolpyruvate synthase by maltose is present in R furiosus.