Extremely thermostable orotidine-5 '-monophosphate decarboxylase from the archaeon Sulfolobus acidocaldarius

Orotidine-5'-monophosphate decarboxylase (E.C. 4.1.1.23) was purified from Sulfolobus acidocaldarius one of the archaea that populates geothermal envi ronments. The enzyme was determined to be a dimer of 22-kDa subunits and wa s readily separated from the oro tate phosphoribosyl transferase of S. acid ocaldarius. The purified orntidine-5'-monophosphate decarboxylase demonstra ted a broad pH optimum centered about pH 8 and an optimal temperature above 98 degrees C. In the absence of substrate and product, however, a consider able thermal inactivation was observed at 85 degrees C or above. To our kno wledge, this is the first orotidine-5'-monophosphate decarboxylase of a hyp erthermophile or an archaeon to be purified. The S. acidocaldarius enzyme m ay offer special advantages for the detailed study of enzyme structure-func tion relationships at extremely high temperatures, due to the fact that eit her loss or gain of function can be genetically selected in vivo. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Sci ence B.V. All rights reserved.