A THERMOSTABLE GLUCOSE-ISOMERASE HAVING A RELATIVELY LOW OPTIMUM PH -STUDY OF ACTIVITY AND MOLECULAR-CLONING OF THE CORRESPONDING GENE

A thermostable glucose isomerase from a newly isolated thermophilic St reptomyces sp. SK strain, had a wide pH range with an optimum of 6 at 60 degrees C and 6.4 at 90 degrees C. It was optimally active at 95 de grees C and completely stable at 80 degrees C for at least 5.5 h with a half-life of 5 h at 90 degrees C. Using E.coli as a host strain and an internal fragment of xylA of S. olivochromogenes as a probe, a 6.5 kb DNA fragment from Streptomyces sp. SK was cloned. This fragment car ries the entire xylA gene since the recombinant plasmid complements th e E.coli xyl-5 mutant strain HB101.