A survey of purine anabolic and catabolic enzymes has resulted in identification of major pathways in schistosome nucleotide biosynthesis. It is shown that multiple pathways for the incorporation of purine bases and nucleosides exist. The evidence suggests that adenosine phosphoribosyltransferase (APRT) activity is about ten times greater than adenosine kinase activity. Furthermore adenosine is converted to AMP principally via the pathway of adenosine deaminase, followed by conversion of inosine to hypoxanthine. In this sequence hypoxanthine phosphoribosyltransferase (HPRT) activity is rate limiting. On the basis of enzyme activities determined, one can suggest candidates of nucleotide analogs which might be useful chemotherapeutic agents.
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