A rapid and sensitive assay for the quantitation of carboxypeptidase N, an important regulator of inflammation

BackgroundCarboxypeptidase N is a plasma zinc metallocarboxypeptidase which is constitutively expressed in the liver and was identified as the enzyme responsible for inactivating bradykinin and kallidin by removing the C-terminal arginine. Because CPN can cleave the C-terminal arginine of C3a, C4a and C5a it is often referred to as anaphylatoxin inactivator. Markedly reduced levels of circulating CPN are associated with recurrent angioedema and abnormal cutaneous polymorphonuclear cell infiltration.MethodsIn this paper we describe a fast kinetic coupled enzymatic assay for the sensitive measurement of carboxypeptidase N activities in serum samples. The assay makes use of the excellent CPN substrate Benzoyl-L-Alanyl-L-Arginine.ResultsThis novel assay is very fast, easy to perform and combines good reliability and reproducibility with excellent correlation with the HPLC-assisted assay (r = 0.927; n = 140).ConclusionThe presented assay can be used for high throughput screening of this important regulator of inflammation in clinical plasma or serum samples.