Bacterial secondary metabolite biosynthetic pathways are frequently encoded in gene clusters. Genomic sequence information allows the identification of likely biosynthetic clusters based on sequence homology to known proteins. Biochemical characterization of suspected biosynthetic enzymes affords the discovery of pathways which may never be identified by traditional screening approaches. In the work presented here, I, in some cases in collaboration with others, characterize the three intragenomic GTP cyclohydrolase II (GCH II) homologs from Streptomyces coelicolor A3(2) and show that one catalyzes a related but distinct reaction from the other two. The basis for the altered activity is investigated and speaks to the chemical mechanism of not only the unusual enzyme but also to all GCH II enzymes. Further, I investigate two other enzymes found in the same gene cluster as the unusual GCH II. Using biochemical techniques, I show that the product of the unusual GCH II is used as a substrate by a creatinine amidohydrolase homolog. Using structural biology, I show that the third enzyme, a 6-pyruvoyltetrahydropterin synthase (PTPS), can not catalyze the PTPS reaction but is capable of binding a pterin substrate. Finally, I propose that the cluster from S. coelicolor containing the unusual GCH II encodes enzymes for a novel pathway to produce a pterin.