Cloning and Expression of the Xylose (Glucose) Isomerase Gene from the Thermophile Thermus thermophilus HB8

Abstract

D-xylose isomerase (E.C. 5.3.1.5) is used industrially to catalyze the isomerization of glucose to the sweeter fructose [1]. The isomerization is reversible and the final fructose content depends on the reaction temperature. At present the process temperature is about 60°C, but a higher temperature would give a higher fructose content. Hence there is a continuing interest in new, stable xylose isomerases [2]. Because thermophilic microorganisms are known to produce highly thermostable enzymes, several thermophiles were screened for isomerase activity. Thermus thermophilus HB8, an aerobe thermophile which grows at temperatures up to 75°C, is the most thermophilic organism from which a xylose isomerase gene has been cloned and characterized [3]. The isomerase has a temperature optimum at 95°C and is more thermostable than any other known isomerase.