part of part of has input has input has output has output process serotonin from L-tryptophan: step 1/2 1 1 1 1 1 1 EC:1.14.16.4 UPa:UER00799 enzymatic_reaction 1 L-tryptophan + 1 O(2) + 1 tetrahydrobiopterin => 1 4a-hydroxytetrahydrobiopterin + 1 5-hydroxy-L-tryptophan. GO:0004510 serotonin from L-tryptophan O(2) L-tryptophan tetrahydrobiopterin 5-hydroxy-L-tryptophan 4a-hydroxytetrahydrobiopterin