Purine nucleoside enzyme that catalyzes the phosphorolysis of adenosine and inosine nucleosides, yielding D-ribose 1-phosphate and the respective free bases, adenine and hypoxanthine (PubMed:31978345). Also catalyzes the phosphorolysis of S-methyl-5'-thioadenosine into adenine and S-methyl-5-thio-alpha-D-ribose 1-phosphate (PubMed:31978345). Also has adenosine deaminase activity (PubMed:31978345). May also act as a polyphenol oxidase: able to oxidize syringaldazine and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) in vitro (PubMed:16740638). adenosine + phosphate = adenine + alpha-D-ribose 1-phosphate phosphate + S-methyl-5'-thioadenosine = adenine + S-methyl-5-thio-alpha-D-ribose 1-phosphate inosine + phosphate = alpha-D-ribose 1-phosphate + hypoxanthine adenosine + H(+) + H2O = inosine + NH4(+) kcat is 1450 min(-1) with 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid as substrate. kcat is 21720 min(-1) with syringaldazine as substrate (at pH 4.5 and 40 degrees Celsius). Optimum pH is 5.5-8.4. Maintains 80% activity at pH 5.0-9.0. Optimum temperature is 44 degrees Celsius. Maintains more than 80% activity at 50 degrees Celsius. Homodimer. Cells lacking this gene are more sensitive to ampicillin, cephradine and cefoxitin than wild-type. Belongs to the purine nucleoside phosphorylase YfiH/LACC1 family.