Abstract
Thermostable purine nucleoside phosphorylases, PUNPI and PUNPII, have been purified from Bacillus stearothermophilus JTS 859. The characterization of PUNPI was reported previously. [Hori et al., Agric. Biol. Chem. 53, 2205 (1989)] PUNPII had a molecular weight of 113, 000, consisting of 4 identical subunits (Mw 28, 000). The isoelectric point was 5.3. The Michaelis constants for inosine, guanosine, and adenosine were 0.22, 0.34, and 0.075 mM, respectively. The optimal temperature of the reaction was 70°C. The enzyme was stable at 70°C. Although other reported purine nucleoside phosphorylases were SH-enzymes, PUNPII was not a SH-enzyme because the enzyme reaction was not inhibited by PCMB and iodoacetic acid, the optimal pH of the enzyme reaction was from 7.0 to 11.0, and the enzyme did not contain cysteine.
PUNPII and PUNPI were different in several points. Not PUNPI but PUNPII could catalyze the phosphorolysis of adenosine. Specific activity of PUNPI and II for inosine were 405 and 50.6μ/min/mg protein at 60°C, respectively. PUNPI was stable at 80°C. PUNPII was stable at 70°C, but was denatured at 80°C.
