[Structural requirements of guanine aminohydrolase (author's transl)].

Structural requirements of substrates and inhibitors of guinea-pig brain guanine aminohydrolase (GAH; E.C. 3.5.4.3), have been established by working with guanine analogs (8-azaguanine, 1-methylguanine, thioguanine and guanosine), purine precursors (5-aminoimidazole-4-carboxamide), purinic bases (xanthine, hypoxanthine, adenine and uric acid) and pyrimidinic bases (citosine, thymine and uracil). The need of the purine ring for the compounds to behave as substrate has been shown. The carbonyl group placed in position 6, plays an essential role in purine and pyrimidine binding to the enzymatic molecule. 5-aminoimidazole-4-carboxamide and allopurinol are enzyme inhibitors, while guanosine, thioguanine and 2,6-diaminopurine are not. Groups in positions 2, 6, 7 and 9 play a significant role in the union of the guanine molecule with guanine aminohydrolase.