Proteinase 3 also known as PRTN3 is an enzyme which in humans is encoded by the PRTN3 gene. PRTN3 is a serine protease enzyme expressed mainly in neutrophil granulocytes. Its exact role in the function of the neutrophil is unknown but in human neutrophils proteinase 3 contributes to the proteolytic generation of antimicrobial peptides. Description: Purulent human sputum. Alternative Names: Proteinase 3, PR-3 protein, PR3 protein, Proteinase 3, Proteinase 3 protein, Proteinase-3, Proteinase-3 protein