Uric Acid Formation

A summary of the steps in the production of uric acid and the genetic diseases associated with deficiencies of specific degradative enzymes are shown in Figure 1. [Note: The bracketed numbers refer to specific reactions in the figure.]

Figure 1:  The degradation of purine nucleotides to uric acid, illustrating some of the genetic diseases associated with this pathway. [Note: The numbers in brackets refer to the corresponding numbered citations in the text.] BMT = bone marrow transplantation; ERT = enzyme replacement therapy; Pi = inorganic phosphate; H2O2 = hydrogen peroxide; NH3 = ammonia.

[1] An amino group is removed from AMP to produce IMP by AMP (adenylate) deaminase or from adenosine to produce inosine (hypoxanthine-ribose) by adenosine deaminase.
[2] IMP and GMP are converted into their respective nucleoside forms, inosine and guanosine, by the action of 5′-nucleotidase.
[3] Purine nucleoside phosphorylase converts inosine and guanosine into their respective purine bases, hypoxanthine and guanine. [Note: A mutase interconverts ribose 1- and ribose 5-phosphate.]
[4] Guanine is deaminated to form xanthine.
[5] Hypoxanthine is oxidized by molybdenum-containing xanthine oxidase (XO) to xanthine, which is further oxidized by XO to uric acid, the final product of human purine degradation. Uric acid is excreted primarily in the urine.