CPN1 encodes the catalytic 50-kDa subunit of carboxypeptidase N (CPN), a plasma zinc metalloprotease that functions as a critical regulator of inflammation and vascular homeostasis 1. The enzyme cleaves carboxy-terminal arginines and lysines from bioactive peptides in circulation, including complement anaphylatoxins, kinins, and other vasoactive substances, thereby modulating their activity and receptor binding 1. CPN1 forms part of a 280-kDa tetrameric complex with two regulatory subunits, and the gene is located on chromosome 10 2. The protein plays a protective role by inactivating potent inflammatory mediators that could otherwise cause tissue damage. Disease relevance includes hereditary angioedema with normal C1 inhibitor, where CPN1 gene variants (c.533G>A, c.582A>G, c.734C>T) are associated with reduced CPN activity (30-50% of normal) and clinical symptoms including angioedema and urticaria 3. CPN1 expression begins early in embryonic development (8.5 days post coitus) in erythroid progenitor cells and hepatocytes 4. Clinically, serum CPN1 levels show promise as a biomarker for breast cancer diagnosis and metastasis assessment, demonstrating superior diagnostic ability compared to CA15-3 alone 5. Additionally, dysregulated CPN1 activity contributes to bradykinin accumulation in severe COVID-19 patients 6.