Combining these insights into an analysis of structure/activity relationships, we revealed that both the succinamic acid and benzimidazole motifs are essential components for mGPDH inhibition by iGPs. Importantly, this analysis identified the benzimidazole ring system as the best candidate for further manipulations to improve both potency and selectivity. In particular, changing or removing the heteroatoms of the imidazole might improve selectivity whereas added substituents to the ring system may provide a means to improve both qualities. We were not able to explore targeted changes to the chemical space occupied by either the linking phenyl group or the succinamide group that did not 410536-97-9 chemical information involve loss of the terminal carboxylic acid. Therefore, these motifs may also provide additional opportunities for improved activity. Enzyme kinetics revealed that iGPs share a common mechanism of mixed inhibition with respect to glycerol 3-phosphate and that potency was governed by subtle Fast Green FCF structural changes. Both iGP- 1 and iGP-5 lowered the maximal activity of mGPDH and increased the Km for glycerol 3-phosphate. Inhibition was enzyme specific, as iGP-1 had no effect on NAD-linked cGPDH activity. This is not surprising considering the two forms are distinct in all respects except their ability to oxidize glycerol 3-phosphate to DHAP. However, this enzyme specificity suggests that iGPs are likely not acting as inhibitory analogs in the substrate binding pocket as described for non-selective inhibitors of both forms such as glyceraldehyde 3-phosphate. The observation of increased Km as well as the lower values for Kic than Kiu indicates that both iGP-1 and iGP-5 have a greater affinity for free enzyme. Both inhibitors have Hill slopes near unity, suggesting they interact with mGPDH at a single, allosteric binding site. Although the analysis of inhibition kinetics was performed in the presence of activating calcium, our evidence from assays of mG
