LNPEP (leucyl and cystinyl aminopeptidase) is a membrane-bound zinc-dependent metalloexopeptidase that functions primarily in the degradation of peptide hormones including oxytocin, vasopressin, and angiotensin IV 1. The enzyme cleaves N-terminal amino acids, particularly before cysteine and leucine residues, and plays a crucial role in maintaining homeostasis during pregnancy through vasopressin inactivation 1. LNPEP is regulated by insulin and colocalizes with GLUT4 in muscle and adipose tissue, where it terminates vasopressin activity at the cell surface 1. Beyond hormone regulation, LNPEP contributes to antigen processing and presentation, particularly in cross-presentation pathways, with expression predominantly in granular layer keratinocytes for processing extracellular antigens 2. The enzyme shows evolutionary conservation across vertebrates, with evidence suggesting its expression in the hypothalamus correlates with behavioral social status in fish 3. Clinically, LNPEP dysfunction is linked to gestational diabetes insipidus and preeclampsia, while its role in accelerated vasopressin degradation during insulin resistance may contribute to hypertension in metabolic syndrome 1. Recent studies also implicate LNPEP in renin-angiotensin system regulation and potential therapeutic targets in cardiovascular disease 4.