1. Measured by its ability to bind biotinylated human LDLR in a functional ELISA. 2. Measured by its ability to bind biotinylated mouse LDLR in a functional ELISA.

Proprotein convertase subtilisin/kexin type 9 (PCSK9), also known as NARC1 (neural apoptosis regulated convertase), which is a newly identified human secretory subtilase belonging to the proteinase K subfamily of the secretory subtilase family. PCSK9 protein is an enzyme which in humans is encoded by the PCSK9 gene with orthologs found across many species. It is expressed in neuroepithelioma, colon carcinoma, hepatic and pancreatic cell lines, and in Schwann cells. PCSK9 protein is highly expressed in the liver and regulates low density lipoprotein receptor (LDLR) protein levels. Inhibition of PCSK9 protein function is currently being explored as a means of lowering cholesterol levels. Thereby, PCSK9 protein is regarded as a new strategy to treat hypercholesterolemia. PCSK9 protein contributes to cholesterol homeostasis and may have a role in the differentiation of cortical neurons.

> 95 % as determined by SDS-PAGE