Purification and comparative properties of a pyrimidine nucleoside phosphorylase from Bacillus stearothermophilus.

The pyrhnidine-nucleoside : orthophosphate ribosyltransferase (EC 2.4.2.2)) or pyrimidine nucleoside phosphorylase, from Bacillus sfearofhermophilus has been purified and compared with similar enzymes from Bacillus subfilis and Escherichia coli. The enzyme is stable at 60°, appears to be induced by either uridine or thymidine, and has a molecular weight of approximately 78,000. Unlike nucleoside phosphorylases from most other sources, the thermophile enzyme catalyzes the phosphorolysis of both thymidine (apparent K, = 3.8 x low4 M) and uridine (apparent K, = 2.5 X 1O-4 M) and, in the synthetic direction, does not distinguish between ribose l-phosphate and deoxyribose l-phosphate. It differs from E. coli and B. subfilis nucleoside phosphorylases in many properties including molecular weight, substrate specificity, thermostability, and induction properties.