This model represents a small clade of purine nucleotide phosphorylases found in certain gamma proteobacteria. The gene is part of an operon for the degradation of xanthosine and is induced by xanthosine. The enzyme is also capable of acting on inosine and guanosine (but not adenosine) in a manner similar to those other phosphorylases to which it is closely related (TIGR01698, TIGR01700).