hypoxanthine , xanthine , guanine and purine ( 1 x 10 ( -1 ) m ) appear to be inhibitors of the pigeon liver pnpase , whereas allopurinol , atp , itp , ctp and utp ( 1. x 10 ( -3 ) m ) do not inhibit the enzyme .
C0034140
purine
C0002144
allopurinol