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. Also catalyzes the phosphorolysis of S-methyl-5'-thioadenosine into adenine and S-methyl-5-thio-alpha-D-ribose 1-phosphate. Also has adenosine deaminase activity