Enteropeptidase (
enterokinase) (EC 3.4.21.9), a highly specific processing
protease, initiating a cascade of reactions activating the digestion
enzymes. Catalyzing
trypsinogen activation
enteropeptidase exhibits unique properties for high efficiency hydrolysis of the
polypeptide chain after lysine-15 residue in the -DDDDK15- sequence. In 1998 we found an unusual
calcium-dependent
autolysis of the
enteropeptidase heavy chain leading to the drastic loss of its activity towards
trypsinogen: after lysine-360 (-NNYEK360-INCN-), -),
arginine-384 (-NEWER384-TQGS-),
arginine-422 (-GRRER422-VGLL-) and
lysine-465 (-QNMEK465-TIFQ-) residues. We used hepta-nona-
peptides as the model substrates for autolysys: human
angiotensin II--DRVYIHPF and cattle
hemoglobin b-chain fragments: LTAEEKA and MLTAEEKAA. Kinetic parameters of
enteropeptidase hydrolysis for these substrates were determined. Recent study demonstrates the ability of
enteropeptidase to hydrolyze
peptide bonds formed by carboxyl groups of Lys or Arg residues if less than four but at least one negative charged
amino acid residue is in any of substrate P2-P5 positions. Ca(2+)-dependent
autolysis of
enteropeptidase heavy chain and of
trypsin were compared; the second one serves as the natural defense mechanism against the undesirable premature
proenzymes activation in pancreas leading to
pancreatitis. The corresponding
enteropeptidase inactivation in low Ca2+ environment ought to be the component of the same protective mechanism.