Uropepsinogen in human urine: its protein nature, activation and enzymatic properties of activated enzyme

Uropepsinogen (UPG) in human urine was highly purified by chromatography on columns of DEAE-lignocellulose, elastin-celite, etc. The purified UPG was composed of two electrophoretically distinguishable components (UPG I and UPG II), and they were isolated in the pure state, respectively. UPG I and UPG II were the same in molecular weight (3.9 X 10(4)) and in N-terminal (leucine) and C-terminal (alanine) amino acid residues. Also, they were quite similar in amino acid composition. They were activated to uropepsin (UP I and UP II, molecular weight, 3.3 X 10(4), respectively), but the activated enzymes were the same in the various properties examined, suggesting that the difference between UPG I and UPG II is due to only a minor change in the peptide segment, perhaps by deamidation. The activation of UPG I and UPG II occurred at acid pHs, the best pH being at 2.0. Both the proenzymes previously incubated with pepstatin at pH 6.8, however, were not activated even in the following incubation at acid sides. The results obtained are discussed in regard to the origin of the proenzyme and its properties before and after activation.

Inhibition of pepsin by analogues of pepsinogen-(1-12)-peptide with substitutions in the 4-7 sequence region

Derivatives of the 1-12 sequence of pig pepsinogen were prepared by solid-phase peptide synthesis. The three derivatives contain substitutions in the 4-7 region of the 1-12 sequence. Glycine was used to replace the hydrophobic residues -Val-Pro-Leu-Val- in pairs. After cleavage and purification, the synthetic peptides were compared with a synthetic peptide of the native sequence, prepared at the same time, with respect to their ability to inhibit the pepsin-catalysed clotting of milk. Inhibitory potency, determined from plots of percentage inhibition versus concentration of synthetic peptide, is inversely correlated with the substitution of glycine residues for the hydrophobic residues. Therefore the equilibrium inhibition of pepsin by these peptides is dominated by the hydrophobic nature of the 4-7 sequence region.

Upg-2: a urinary pepsinogen variant located on chromosome 1 of the mouse

Acrylamide gel electrophoresis of mouse urine distinguishes two groups of pepsinogens, the fast-migrating group A and the slow-migrating group B. Inbred mouse strains fall into two categories with respect to group B pepsinogens, one expressing a single-banded and the other a double-banded phenotype. This variation is controlled by a single locus, urinary pepsinogen-2 or Upg-2, which has at least two alleles, Upg-2s and Upg-2d. Typing of recombinant inbred strains suggests that the location of the Upg-2 locus is on chromosome 1, in the vicinity of loci coding for other peptidases, namely, Pep-2 and Rnr, and of the Acf-1 locus.

Rat gastric prepepsinogen: in vitro synthesis and partial amino-terminal signal sequence

The major translation product of rat gastric mucosa RNA in a wheat germ cell-free system was identified as prepepsinogen by electrophoretic analysis of its immunoprecipitate on sodium dodecyl sulfate (SDS)-polyacrylamide gels and amino-terminal sequence determination. The translation product containing radioactive amino acids, purified by SDS-polyacrylamide gel electrophoresis, was shown to have an amino-terminal extension peptide comprising 16 amino acid residues. A partial amino acid sequence of this extension peptide is as follows: Met-X-X-Met-Val-Val-X-Leu-Leu-X-Leu-X-Leu-Leu-X-X-pepsinogen.