Hepsin, also known as TMPRSS1, is a Type II membrane protein with an extracellular serine protease domain. It is most highly expressed in liver, but is also present in many other tissues, notably lung, kidney, and skeletal muscle. A soluble form of Hepsin lacking the transmembrane domain has been identified. Hepsin is capable of activating Factor VII, and may initiate blood coagulation at the cell surface. Hepsin is overexpressed in various human tumors, including prostate, and is considered to be a biomarker for prostate cancer. rhHepsin was expressed as a secreted, soluble protein lacking its cytosolic and transmembrane domains. The D161E and R162K mutations were introduced into the prosequence to improve expression of the rhHepsin.