binding tetrahydrobiopterin binding BH4 binding Binding to a tetrahydrobiopterin, 5,6,7,8-tetrahydrobiopterin or a derivative thereof; tetrahydrobiopterins are enzyme cofactors that carry electrons in redox reactions. molecular_function sapropterin binding GO:0034617 Reactome:R-HSA-1497784 H4biopterin binding Reactome:R-HSA-1497796