text: * A nuclease frees the nucleotide
  ** A nucleotidase creates adenosine, then adenosine deaminase creates inosine
  ** Alternatively, AMP deaminase creates inosinic acid, then a nucleotidase creates inosine
  * Purine nucleoside phosphorylase acts upon inosine to create hypoxanthine
  * Xanthine oxidase catalyzes the biotransformation of hypoxanthine to xanthine
  * Xanthine oxidase acts upon xanthine to create uric acid