Hypoxanthine-guanine phosphoribosyltransferase (HGPRT, EC 2.4.2.8) from a newly characterized thermophile Thermoanaerobacter tengcongensis was expressed in Escherichia coli and purified. Analytical get filtration suggested that the enzyme exist as a homotetramer in solution. The optimal pH for the forward reaction was found to be 8.0 and the optimal temperature 70degreesC. The steady-state kinetic characteristics suggest that hypoxanthine is the most effective substrate. This enzyme showed a half-life of 75 min at 50degreesC and no apparent loss of activity after 3 months at 4degreesC. (C) 2003 Elsevier Inc. All rights reserved.