PRSS (Protease; serine) genes produce three isoforms of pancreatic trypsinogen. Based on their electrophoretic mobilities, they are named cationic trypsinogen (trypsin 1/PRSS1), anionic trypsinogen (trypsin 2/PRSS2) and meso- (or "in the middle") trypsinogen (trypsin 3/PRSS3). PRSS1 is the predominant form (67%). Following secretion from the pancreas, active trypsin is generated in the duodenum through the interaction of brush-border duodenal enterokinase with trypsinogen.