C9orf3 is an aminopeptidase and belongs to the M1 family of metallopeptidases or gluzincins. Aminopeptidases catalyze the hydrolysis of amino acid residues from the N-terminus of peptide or protein substrates. C9orf3 is able to cleave angiotensin III to generate angiotensin IV, a bioactive peptide of the renin-angiotensin pathway but not able to cleave angiotensin I and angiotensin II. It may play a role in the proteolytic processing of bioactive peptides in tissues where it is expressed. C9orf3 is predominantly expressed in pancreas, placenta, liver, testis and heart and at lower level in brain, lung and kidney. There are four named isoforms.