Isolation of human, swine, and rat prepepsinogens and calf preprochymosin, and determination of the primary structures of their NH2-terminal signal sequences

Correlation between a proteolytic method and a radioimmunoassay for porcine serum pepsinogen concentrations

The measurement of serum pepsinogen concentrations by enzymatic method and immunoassay provides diagnostic values and should be helpful in the detection of gastric diseases related to a rise of blood pepsinogen. In the present study, the correlation between a conventional enzymatic method and a recently developed radioimmunoassay (RIA) for serum pepsinogen A was investigated. A total of 123 sera samples of porcine foetuses (n = 28), adult healthy pigs (n = 56), pigs with parakeratosis (n = 25) and pigs with ulceration of the pars oesophagea (n = 14) were tested. Overall, there was a slight correlation between the two methods (r = 0.60). In relation to individual animal groups, the correlations (r) were 0.39 (P>0.05), 0.74 (P<0.001), 0.19 (P>0.05) and 0.34 (P>0.05) in foetuses, healthy pigs, pigs with parakeratosis and pigs with ulcers, respectively. In both methods, pepsinogen concentrations (means+/-SE) were significantly higher (P<0.05) in pigs with parakeratosis (1778 +/- 86.00 mUTyr/L; 690 +/- 53.00 ng/mL) and in pigs with ulcers (2026 +/- 153.00 mUTyr/L; 1747 +/- 94.00 ng/mL) when compared to healthy pigs (935 +/- 58.00 mUTyr/L; 275 +/- 35.00 ng/mL). The proteolytic method gave a significant increased activity (P<0.05) in foetuses (1150 +/- 82.00 mUTyr/L) vs. (935 +/- 58.00 mUTyr/L) in healthy adult pigs, indicating an additional proteolytic activity in the sera of foetuses or neonates.

Nucleotide sequence and expression in Escherichia coli of cDNA of swine pepsinogen: involvement of the amino-terminal portion of the activation peptide segment in restoration of the functional protein

A clone, pSPcA2, which carries the full-length swine pepsinogen cDNA was isolated. The coding sequence comprised the signal peptide [15 amino acids (aa)], the activation peptide segment (44 aa) and mature pepsin (327 aa). The deduced amino acid sequence agrees with the published sequence with two exceptions. Asparagine instead of aspartate is present at aa positions 19 and 308. Two types of plasmids, pAS and pUCtacSPc series, were constructed for expressing swine pepsinogen cDNA. These plasmids directed the synthesis of polypeptides which were detected by employing an antibody to swine pepsinogen. However, all the polypeptides formed aggregates and showed no acid protease activity. Only the protein directed by pAS5 regained the acid protease activity after renaturation procedures. The activity was completely inhibited by pepstatin. Furthermore, the renatured pAS5 protein was spontaneously converted to pepsin under acidic conditions. The presence of Arg-8 in the activation peptide segment appears important for the stabilization of the pepsinogen molecule.

Nucleotide sequence of a nearly full-length cDNA coding for pepsinogen of rat gastric mucosa

A nearly full-length rat pepsinogen cDNA was isolated from a rat gastric mucosa cDNA library and its nucleotide sequence was determined. The cDNA comprises 1370 base pairs (bp), including the 5'-non-coding region (60 bp), the coding nucleotide sequence (1176 bp) and the 3'-non-coding region (131 bp). The predicted amino acid sequence of rat prepepsinogen (392 residues) contains a 16-residue signal sequence followed by the pepsionogen moiety of 376 residues. Rat pepsinogen has an amino acid composition characteristic of C-type pepsinogens and is much more homologous in amino acid sequence with C-type pepsinogens than A-type pepsinogens. These results indicate that the major form of rat pepsinogen can be classified as a C type pepsinogen.