The gene encoding ribose phosphate pyrophosphokinase (Pk-RPPK) from a hyperthermophilic archaeon, Pyrococcus sp. KOD1 (Pk), was cloned, sequenced and expressed in Escherichia coli. The recombinant Pk-RPPK (280 aa, 31,113 Da) was purified to homogeneity. The optimal temperature and pH for the enzymatic activity are 50 degrees C and 7.0, respectively. The half-life of the enzymatic activity is 55 min at 70 degrees C. A unique characteristic of the enzyme is that it can utilize CTP and GTP as substrates In addition to ATP. It was also found that Co2+ in particular and Ni2+ markedly enhance the specific activity of the enzyme, as does Mg2+ in the presence of Co2+ (182 units/mg protein).