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Purine synthesis pathways

De novo synthesis involves formation, in ten steps, of inosine monophosphate from phosphoribosylpyrophosphate (PRPP). Interconversion of inosine monophosphate into guanosine monophosphate and adenosine monophosphate both occur in two steps. (1) adenylosuccinate lyase; (2) 5'-nucleotidase(s); (3) adenylosuccinate synthetase; (4) AMP deaminase; (5) adenosine deaminase; (6) adenosine kinase; (7) hypoxanthine-guanine phosphoribosyltransferase; (8) adenine phosphoribosyltransferase; (9) xanthine oxidase. The enzyme defect is indicated by solid bars. (Contributed by Dr. Georges Van den Berghe.)