N. Yahagi et al., COMPLEMENTARY-DNA CLONING AND SEQUENCING OF RAT ENTEROPEPTIDASE AND TISSUE DISTRIBUTION OF ITS MESSENGER-RNA, Biochemical and biophysical research communications, 219(3), 1996, pp. 806-812
A cDNA clone encoding enteropeptidase (EC 3.4.21.9), a key enzyme for
the conversion of trypsinogen to trypsin, was isolated from a rat duod
enal mucosa cDNA library. Sequence of the 3585 base pair clone predict
ed that enteropeptidase is synthesized as a single-chain precursor for
m, proenteropeptidase, consisting of 1058 amino acid residues with an
internal signal sequence (51 residues) and is then processed into the
mature enzyme consisting of three different peptide chains, i.e., mini
, light and heavy chains, not the previously reported two-chain enzyme
. The structure of enteropeptidase is relatively conserved among diffe
rent species and the rat enteropeptidase is 24 and 39 amino acids long
er than the porcine and human ones, respectively. Northern blot analys
is of RNAs from normal rat tissues revealed that the enteropeptidase m
RNA of around 4.4 kb in size was expressed only in the duodenal mucosa
, and high proteolytic activity of the enzyme was detected in the prox
imal small intestine. Additional analysis of the RNAs by RT-PCR reveal
ed that a low level of the mRNA was also expressed in the other parts
of the small intestine, i.e., jejunum and ileum. These results indicat
e that the biosynthesis of enteropeptidase takes place mainly in the p
roximal small intestine, the duodenum, and the importance of the regio
n in the physiology of intestinal protein digestion regulated by the e
nzyme is suggested. Furthermore a faint signal of the mRNA was also de
tected in the stomach, colon and brain in which the existence of tryps
in-like serine proteases were reported. The significance of the low le
vel expression of the gene is unclear, but the potential peptide-proce
ssing function of the enzyme in these tissues is also suggested. (C) 1
996 Academic Press, Inc.