The amino terminal sequences of acid proteases-human pepsin and gastricsin and the protease of Rhizopus chinensis

Human pepsinogen C (progastricsin) polymorphism: evidence for a single locus located at 6p21.1-pter

A series of six clones containing the entire human pepsinogen C gene (PGC) was identified in a cosmid vector library by using cDNA and oligonucleotide probes. The 10.7-kb PGC gene includes nine exons and exhibits a high degree of sequence identity (60%) with the functionally related pepsinogen A genes. The predicted amino acid sequence was identical with the partial amino-terminal and carboxyl-terminal sequences of purified pepsinogen C. An informative restriction fragment length polymorphism was detected with several restriction enzymes and involved an insertion or deletion of 100 bp of intron sequence located between exons 7 and 8. Evidence that there is only a single PGC gene in humans is presented. The PGC gene and the prolactin gene were regionally localized to 6p21.1-pter by analysis of mouse X human somatic cell hybrids.

The N-terminal sequence of rat pepsinogen

The amino-acid sequence of 96 residues in the N-terminal region of rat pepsinogen I was determined and the first 46 residues were found to constitute the activation peptide segment. There was high degree of homology between the activation segments of rat pepsinogen and some pepsinogens A (pig, cow, Japanese monkey and human). However, the number of residues substituted between rat and the other pepsinogens were considerably larger than those among pepsinogens A. In the N-terminal 24 residues of active pepsin, homology (88%) between rat pepsin and human gastricsin was higher than that (50%) between rat pepsin and pepsin A from human or pig. This strongly suggests that rat pepsin should be classified as pepsin C.

Photoaffinity reagents for use with pepsin and other carboxyl proteases

Two compounds have been designed to serve as photoaffinity reagents for use with carboxyl proteases. 1,2-Epoxy-3-(4'-azido-2'-nitrophenoxy)propane has been synthesized and shown to react with porcine pepsin in the same fashion as the traditional inhibitor 1,2-epoxy-3-(p-nitrophenoxy)propane, while p-azidophenacyl bromide is similar to other phenacyl bromides in its reaction with pepsin. In combination with p-azido-alpha-diazoacetophenone, previously shown to resemble alpha-diazo carbonyl reagents in its reaction with pepsin, photoaffinity analogs are now available for all three of the widely-used carboxyl protease inhibitors.

Radioimmunoassay of group II pepsinogen in human serum

A new radioimmunoassay (RIA) using a double antibody method for human Group II pepsinogens in serum was developed. (1) Sensitivity of this assay system was of the order of 1 microgram per 1 of serum and optimal assay range was 10 to 50 microgram per 1; (2) no effect of interference of human serum was detected and there was no cross-reaction with human Group I pepsinogens within the optimal assay range; (3) satisfactory results were obtained for both within- and between-assay reproducibility (coefficient of variation was 3.9% and 3.7-15.3%, respectively); (4) the mean (+/- SEM) serum Pg II level in healthy donors was 15.9 +/- 0.7 microgram/l for males and 12.8 +/- 1.3 microgram/l for females; the difference between males and females was statistically significant (p less than 0.05); (5) the mean serum Pg II level in 10 patients with total gastrectomy was 1.2 +/- 0.05 microgram/l. These results suggest that most of Pg II in human serum is derived from the gastroduodenal system.

alpha-Bromo-4-amino-3-nitroacetophenone, a new reagent for protein modification. Modification of the methionine-290 residue of porcine pepsin

A new coloured reagent for protein modification, alpha-bromo-4-amino-3-nitroacetophenone (NH2BrNphAc), was synthesized. The reagent was found to alkylate specifically the methionine-290 residue of porcine pepsin below pH 3 at 37 degrees C, which lead to a 45% decrease of enzyme's activity towards haemoglobin. The effect of this reagent as well as that of other phenacyl bromides on the activity of pepsin appeared to be a result of steric hindrance caused by the attachment of bulky reagent residue to the edge of the cleft harbouring the enzyme active site. Only marginal reaction with the co-carboxy group of aspartic acid-315 was found under the above conditions. More pronounced esterification of carboxy groups (up to one residue per enzyme molecule) occurred when the pH was shifted to 5.2. The latter modification had no noticeable effect on enzyme activity, thus disproving a previously held assumption that pepsin inactivation by phenacyl bromide is due to the carboxy-group esterification. alpha-Bromo-4-amino-3-nitroacetophenone forms derivatives with characteristic u.v. spectra when it reacts with methionine, histidine, aspartic and glutamic acid residues, and may be recommended as a reagent for protein modification.

A novel method for converting apolipoprotein B, the major protein moiety of human plasma low density lipoproteins, into a water-soluble protein

We have developed a new technique to solubilize apolipoprotein B (ApoB) in aqueous solutions. The procedure involves stirring ApoB in 6 M guanidine/20 mM NH4Cl/NH4OH in the presence of cupric ammonia complexes at pH 9.7 for 20 h in N2, and then removing these reagents by a series of dialysis in N2. The resulting Cu(NH3)4(2)+-treated (Cu2+-treated) ApoB is soluble in aqueous buffers of pH above 8.3 or below 3. Parallel experiments carried out on control proteins, human albumin, alpha-lactalbumin, and insulin, indicated no change in molecular weight and no creation of a new NH2-terminal amino acid after Cu2+-treatment. By Edman degradation, the Cu2+-treated ApoB showed no detectable NH2-terminal amino acid. These results showed that the mechanism of Cu2+-solubilization of ApoB was not due to the cleavage of peptide bonds. Electrophoresis on urea-polyacrylamide gel, Cu2+-treated ApoB showed the same number of bands as the non-treated ApoB in the separating gels (7%) near the cathode, suggesting the heterogeneity of ApoB. In SDS-polyacrylamide gel (10%), the reduced and Cu2+-treated ApoB migrated with the similar mobilities to the monomer or dimer of human albumin. Antibodies raised against Cu2+-treated ApoB gave at least two immunoprecipitin lines against the Cu2+-treated ApoB as well as the non-treated guanidine-HCl-soluble ApoB, suggesting the presence of non-identical subunits.

Isorenin, pseudorenin, cathepsin D and renin. A comparative enzymatic study of angiotensin-forming enzymes

1. Renin was purified 30 000-fold from rat kidneys by chromatography on DEAE-cellulose and SP-Sephadex, and by affinity chromatography on pepstatinyl-Sepharose. 2. The enzymatic properties of isorenin from rat brain, pseudorenin from hog spleen, cathepsin D from bovine spleen, and renin from rat kidneys were compared: Isorenin, pseudorenin and cathepsin D generate angiotensin from tetradecapeptide renin substrate with pH optima around 4.9, renin at 6.0. With sheep angiotensinogen as substrate, isorenin, pseudorenin and cathepsin D have similar pH profiles (pH optima at 3.9 and 5.5), in contrast to renin (pH optimum at 6.8). 3. The angiotensin-formation from tetradecapeptide by isorenin, pseudorenin and cathepsin D was inhibited by albumin, alpha-and beta-globulins. These 3 enzymes have acid protease activity at pH 3.2 with hemoglobin as the substrate. Renin is not inhibited by proteins and has no acid protease activity. 4. Renin generates angiotensin I from various angiotensinogens at least 100 000 times faster than isorenin, pseudorenin or cathepsin D, and 3000 000 times faster than isorenin when compared at pH 7.2 with rat angiotensinogen as substrate. 5. The 3 'non-renin' enzymes exhibit a high sensitivity to inhibition by pepstatin (Ki less than 5.10(-10) M), in contrast to renin (Ki approximately 6-10(-7) M), at pH 5.5. 6. It is concluded from the data that isorenin from rat brain and pseudorenin from hog spleen are closely related to, or identical with cathepsin D.

Homology among acid proteases: comparison of crystal structures at 3A resolution of acid proteases from Rhizopus chinensis and Endothia parasitica

The molecular structures of two fungal acid proteases at 3 A resolution have been compared, and found to have similar secondary and tertiary folding. These enzymes are bilobal and have a pronounced cleft between the two lobes. This cleft has been identified as the active site region from inhibitor binding studies. The results of the comparison are discussed in terms of homology among the acid proteases in general.

Comparison of the primary structures of acidic proteinases and of their zymogens

From the scattered information about primary structures of aspartate proteinases the following general features appear: 1) Sequence determinations show that two catalytically active aspartic acid residues are located in highly conservative surroundings. 2) Zymogens have so far only been found for extracellular aspartate proteinases of the vertebrates. The zymogens from the gastric mucosa are converted into active enzymes by a limited proteolysis releasing 42 to 44 residues from the NH2-terminus. A common pattern of basic and apolar residues is observed in this NH2-terminal segment. 3) In the presently known structures gastric proteinases and their zymogens have about 40% of all residues in common. The sequence of penicillopepsin shows 18% of identity with the gastric proteinases.

The crystal structure of an acid protease from Rhizopus chinensis at 2.5 A resolution

This paper contains a preliminary report of the crystal structure of the acid protease from Rhizopus chinensis at 2.5 A resolution. The molecule is bilobal with a large cleft between the lobes. Pepstatin binds in the cleft near the catalytically active Asp-35. The overall folding of the molecule consists primarily of antiparallel beta-strands, there being only four small helices.