Catabolism of pteridine cofactors

By measuring excreted radioactivity the retention of 14C-labeled tetrahydropterins (biopterin, d-erythro- and l-erythro-nepterin, 6-hydroxymethylpterin) and of 7,8-dihydro-6-hydroxymethylpterin has been followed after intraperitoneal injection into rats, given at a concentration of 10 mg/kg. More than 70% of the reduced 6-polyhydroxyalkylpterins are retained. In the urine 6-hydroxylumazine and xanthopterin are found as the main degradation products of all the reduced pterins. No radioactivity was incorporated into biopterin, isolated from the urine after injection of either tetrahydroneopterin, 7,8-dihydro- or tetrahydro-6-hydroxymethylpterin.