Suramin Discriminates Between the Calmodulin-Binding Sites of Neuronal and Inducible Nitric Oxide Synthase
McNamara, Alyssa L.
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Nitric oxide synthase (NOS) continues to be at the center of several studies as it is a formidable target for drug design. Nitric oxide (∙NO), the product of the NOS reaction, is linked to a number of pathological conditions. Suramin is a polysulfonated naphthylurea that has specifically been shown to discriminate among calmodulin-‐binding sites on proteins. In the current study, suramin was shown to inhibit both neuronal NOS and inducible NOS, however, it was found to have a greater effect on inducible NOS. Kinetic analysis showed that the IC50 for the inducible NOS, in the absence of EDTA is approximately 41 μM, but in the presence of 1 mM EDTA, is 2.6 μM. IC50 of the neuronal NOS was found to be between 60 and 100 μM. These data suggest that suramin distinguishes between the inducible and the neuronal NOS. Western analysis further suggests that suramin’s distinction of the NOS forms may occur through its interaction at the calmodulin-‐binding sites. Docking studies indicate that suramin binds to the inducible NOS calmodulin-‐ binding site with a binding energy of -‐14.32 kcal/mol. These results point to a new NOS target site for drug design.