In one path: a nucleotidase creates adenosine, and adenosine deaminase creates inosine (the deficiency of this enzyme is a cause of severe combined immunodeficiency)
In the other path: AMP deaminase creates IMP, and a nucleotidase creates inosine
Purine nucleoside phosphorylase acts upon inosine to create hypoxanthine
Xanthine oxidoreductase acts upon hypoxanthine to create xanthine
Xanthine oxidoreductase acts upon xanthine to create uric acid
High levels of uric acid can predispose to gout when the acid crystalises in joints; this phenomenon only happens in humans and some animal species (e.g. dogs) that lack an intrinsic uricase enzyme that can further degrade uric acid into 5-Hydroxyisourate.
Purines from turnover of nucleic acids (or from food) can also be salvaged and reused in new nucleotides.
The enzyme adenine phosphoribosyltransferase (APRT) salvages adenine.
The enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT) salvages guanine and hypoxanthine. (Genetic deficiency of HPRT causes Lesch-Nyhan syndrome.)