Use of electrospray mass spectrometry to directly observe an acyl enzyme intermediate in β‐lactamase catalysis

Electrospray mass spectrometry was used to directly observe intact acyl enzyme complexes formed between a class C beta-lactamase (from Enterobacter cloacae P99) and four poor substrates/inhibitors. In each case the molecular weight difference between the unreacted and the reacted beta-lactamase was consistent with the formation of an acyl enzyme.