The principal action of the enterokinase present in the human intestinal juice is to

Enterokinase, also known as enteropeptidase, is a proteolytic enzyme produced by the mucosal glands of the duodenum in the small intestine [t1][t5]. Its primary physiological role is the activation of trypsinogen, an inactive zymogen secreted by the pancreas [t5][t7]. Enterokinase cleaves a specific peptide bond at the N-terminal end of trypsinogen to convert it into active trypsin [t4][t6]. Once trypsin is formed, it initiates a cascade by activating other pancreatic zymogens like chymotrypsinogen and pro-carboxypeptidase [t1][t4]. While other enzymes like pepsin or rennin hydrolyse casein into paracasein in the stomach [t4][t8], and carboxypeptidases act on terminal peptide bonds [t4], enterokinase specifically serves as the 'master switch' for pancreatic juice activation in the intestinal lumen [t3][t6].

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC10191478/
2. [2] https://en.wikipedia.org/wiki/Trypsinogen