Instead of using the lipid II substrate that requires prior labelling with a radioactive isotope or fluorophore to probe the formation of peptidoglycan in bacterial transglycosylation, the released undecaprenyl pyrophosphate (UPP) product is quantitatively measured either using a terpyridine–zinc fluorescence turn-on sensor or simply by the second-order scattering effect of the in situ formed UPP–calcium complex. Both the assay methods are utilized to identify moenomycin A as a potent transglycosylase inhibitor with a consistent IC50 value.
