Nitrocefin (CAS 41906-86-9) is a chromogenic cephalosporin substrate commonly employed in biochemical assays to detect β-lactamase enzymatic activity. β-lactamases, enzymes prevalent in microbial species, catalyze the hydrolysis of β-lactam antibiotics such as penicillins and cephalosporins, causing antibiotic resistance. Upon cleavage by β-lactamase enzymes, nitrocefin undergoes a measurable colorimetric shift from yellow to red, enabling visual or spectrophotometric detection in the range of approximately 380–500 nm. Nitrocefin prominently serves in microbiological and clinical research to evaluate resistance profiles of bacterial isolates and in assays for inhibitor activity toward β-lactamases. Its reported IC50 varies depending on β-lactamase type, concentration, and assay conditions, with typical values ranging from approximately 0.5 to 25 μM.

Reference:
[1] O'Callaghan, Cynthia H et al.  Novel Method for Detection of B-Lactamases by Using a Chromogenic Cephalosporin Substrate. Antimicrobial Agents and Chemotherapy. 1972 Apr; 1(4):283-288.