Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P00790 (PGA)
 2,475 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pepsin was spin-labelled with N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidyl) bromoacetamide, possibly at the active site, at a beta-catboxyl group of a reactive aspartic acid. The spectrum of the spin-labelled pepsin showed that the spin probe was strongly immobilized (correlation time is greater than or equal to 10(-8) sec). Spin-labelled pepsin was thermally denatured at various temperatures and electron paramagnetic resonance (e.p.r.) spectra were taken at various times. Rates of denaturation estimated from the e.p.r. spectra at various temperatures showed that the enthalpy and entropy of thermal denaturation of spin-labelled pepsin at pH 3.5 were 48.0+/-4.9 kcal/mole and 214.7+/-14.5 e.u. respectively. Addition of conc. NaOH or 1 M acetate buffer at pH 6.0 sharpened e.p.r. spectra of the spin-labelled pepsin, indicating that the spin probe became mobilized by alkaline denaturation. Addition of urea caused unfolding of the protein which increased with the urea concentration, although only slight transition of conformational changes was observed in the e.p.r. spectra.
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PMID:Electron paramagnetic resonance studies on spin-labelling of pepsin: effects of temperature, pH and urea on its conformation. 0 80

To understand more directly the tissue defect in osteogenesis imperfecta (OI), bone matrix was analyzed from an infant with lethal OI (type II) of defined mutation (collagen alpha 2(I)Gly580-->Asp). Pepsin-solubilized alpha 1(I) and alpha 2(I) chains and derived CNBr-peptides migrated more slowly on sodium dodecyl sulfate-polyacrylamide gel electrophoresis compared with normal human controls. The peptide alpha 2(I)CB3,5, predicted to contain the mutation site, ran as a retarded doublet band and was purified by high performance liquid chromatography and digested with V8 protease. Two peptides with amino-terminal sequences beginning at residue 576 of the alpha 2(I) chain were isolated. One had the normal sequence. The other differed in that aspartic acid replaced glycine at residue 580 as predicted from cDNA analysis, and in having an unhydroxylated proline at residue 579. From yields on microsequencing and the relative intensities of the two forms of alpha 2(I)CB3,5 on SDS-polyacrylamide gel electrophoresis, the ratio of mutant to normal alpha 2(I) chains in the infant's bone matrix was 0.7/1. Although the effects of an efficient incorporation of mutant chains on the properties of the bone matrix are unknown, it may be that in this OI case the tissue abnormalities result more from the presence of mutant protein than from an underexpression of matrix.
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PMID:Incorporation of type I collagen molecules that contain a mutant alpha 2(I) chain (Gly580-->Asp) into bone matrix in a lethal case of osteogenesis imperfecta. 138 13

L-Aspartate and L-serine were found to undergo amino acid racemization in brain myelin basic protein (MBP) of aging humans. The observed racemization was different in each chromatographically purified MBP isoform. Pepsin digestion of MBP produced three peptides, each of which exhibited different degrees of racemization of the same amino acids. MBP isolated by the same method from rat and guinea pig brain showed little accumulation of D-amino acids. Total MBP isolated from SDS-polyacrylamide disc gel electrophoresis of total human myelin proteins (delipidated myelin) was racemized to the same extent as purified MBP, indicating that the racemization observed was not an artifact of the isolation procedure. Myelin proteolipid protein from the same gel was racemized approximately half as much as MBP. The age and environment of the aspartates and serines in myelin proteins may strongly affect their observed racemizations.
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PMID:Differential racemization of aspartate and serine in human myelin basic protein. 244 3

Human pepsinogen A3 and A5 have been purified to chromatographic and electrophoretic homogeneity. At pH 2 pepsinogen A3 activates at a much faster rate than pepsinogen A5. Leu-23-Lys-24 is the first bond cleaved during activation of pepsinogen A3. This bond is also cleaved in pepsinogen A5, but together with the cleavage of Asp-25-Phe-26. Amino acid sequencing shows that pepsinogen A3 has Glu at position 43, whereas pepsinogen A5 has Lys.
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PMID:Activation of human pepsinogens. 319 40

Pepsin-solubilized collagen VI was prepared from human placenta and used to separate three constituent chains for determining partial amino acid sequences. Antibodies raised against the chains assisted in the identification and purification of several cDNA clones from three expression lambda gt11 libraries. Most of the clones hybridized to either a 3.5-kb or 4.2-kb mRNA species which by matching peptide and nucleotide sequences could be identified as coding for the alpha 2(VI) or alpha 1(VI) chain, respectively. Other clones hybridized to either an 8.5-kb mRNA which very likely encoded the alpha 3(VI) chain or to an unknown 2.0-kb mRNA. Northern blots revealed a considerable variation in the mRNA levels for each collagen VI chain in both skin and cornea fibroblasts and in several tumor cell lines. Limited sequence data generated from peptides and cDNA clones demonstrated a characteristic cysteine pattern at the junction between N-terminal globular domain and triple helix in all three chains. In addition, the data showed occasional interruptions of triplet sequences within the triple-helical domain and the presence of two Arg-Gly-Asp sequences which are potential cell-binding structures.
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PMID:Characterization of three constituent chains of collagen type VI by peptide sequences and cDNA clones. 366 27

Apolipoprotein AI of human high-density lipoproteins is secreted by hepatocytes as a proapolipoprotein with a N-terminal hexapeptide sequence (Arg-His-Phe-Trp-Gln-Gln-) which differs from the prosequence of rat apolipoprotein AI (Trp-Asp-Phe-Trp-Gln-Gln). The two proteins have in common the unusual cleavage site -Gln-Gln-Asp-Glu-. It is hydrolysed by a specific serum proteinase with the release of mature apo AI. We synthesized a model substrate for the study of the final processing of pro-apo AI by the serum proteinase. It is an undecapeptide embracing the human pro-hexapeptide sequence and the first five N-terminal residues of apo AI, covalently linked to a hydrophilic resin. The N-terminal arginine residue was 3H-labelled. [formula; see text] This sequence was not cleaved by human serum under the conditions under which rat serum processes the pro-form of apo AI secreted by rat hepatocytes. Pepsin and chymotrypsin fragmented the undecapeptide at sites characteristic for these proteinases. We conclude that the proteolytic cleavage at the specific site (-Gln-Gln-Asp-Glu-) requires the correct conformation in addition to the specific amino-acid sequence.
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PMID:Processing of proapolipoprotein AI requires specific conformation. 392 Oct 42

Pepsin reacts stoicheiometrically with the active-site-directed irreversible inhibitor N-diazoacetyl-l-phenylalanine methyl ester, with concomitant loss of all proteolytic and peptidolytic activity. The reagent esterifies a unique aspartic acid residue in pepsin, which is in the sequence:Ile-Val-Asp-Thr-Gly-Thr-Ser
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PMID:An aspartic acid residue at the active site of pepsin. The isolation and sequence of the heptapeptide. 489 1

The pools of Arg, Gly, His, Ile, Ser, Glu, Leu, Val and Asp were lower during photosynthesis at 1% O2 concentration. At the same time specific radioactivity of a number of amino acids--following 14CO2 incorporation--was different than that at atmospheric O2 concentration. This is probably due to the inhibition of the photorespiratory nitrogen cycle and the resulting NH+4 deficiency. The pattern of response to O2 concentration suggests that in rye plants in the light, all Gly and a part of Ser are synthesized by an O2-sensitive pathway, i.e. via the glycolate pathway, but most of Ser is probably formed from 3-phosphoglycerate (3-PGA) via the O2-insensitive pathway. Changes in the pool size and specific radioactivity after 6 h incubation in darkness suggest that synthesis of Gly is strongly light-dependent, whereas synthesis of Ser was substantial also in darkness. The specific radioactivity of Ala, Asp, Ser and Glu indicates that in darkness those amino acids are formed from a common precursor, i.e. glycolytic 3-PGA, and undergo rapid metabolic turnover.
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PMID:Photosynthesis in detached rye leaves at normal and low oxygen concentration. II. Incorporation of 14CO2 into amino acids. 681

Pepsin-catalyzed synthesis of protected peptides was studied in two-phase systems containing up to 5% (by volume) of aqueous phase. A methodological study was carried out to determine the optimum conditions for the synthesis of the model protected peptide Z-Phe-Phe-OMe. Several parameters such as concentrations of carboxylic and amino components, pH of the aqueous phase, ratio of organic to aqueous phase volumes and nature of the organic solvent were investigated. It was observed that the most hydrophobic solvents produced the best yields, despite the low solubility of substrates in these media. The log P of the solvent could be used to predict the solvent effect over the reaction yields. Pepsin immobilized by adsorption onto the solid supports Celite and Chromosorb was employed to perform a study of secondary specificity of the enzyme in organic media through the coupling between Z-X-Phe-OH (X = Ala, Asp, Glu, Gly, Phe, Ile, Val, Trp and Tyr) and Phe-OMe. This investigation was performed in two solvent systems: (A) ethyl acetate:citrate buffer pH 4.5 (98:02, v:v) and (B) acetonitrile:citrate buffer pH 4.5 (96:04, v:v). Reaction rate data showed that pepsin had a preference for more hydrophilic substituents in the P2 position. These data are in contrast to the literature for a similar reaction performed in predominantly aqueous media. Thus, for mainly organic media, partition phenomena are very important and may cause an apparent modification of enzyme specificity.
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PMID:Pepsin-catalyzed peptide synthesis in organic media: studies with free and immobilized enzyme. 789 3

The equilibrium mixture of yeast enolase with substrate, 2-phospho-D-glycerate (2-PGA), and product, phosphoenolpyruvate (P-enolpyruvate), has been crystallized from solutions of poly(ethylene glycol) (PEG) at pH 8.0. Crystals belong to the space group C2 and have unit cell dimensions a = 121.9 A, b = 73.2 A, c = 93.9 A, and beta = 93.3 degrees. The crystals have one dimer per asymmetric unit. Crystals of the equilibrium mixture and of the enolase complex of phosphonoacetohydroxamate (PhAH) are isomorphous, and the structure of the former complex was solved from the coordinates of enolase-(Mg2+)2-PhAH [Wedekind, J. E., Poyner, R. R., Reed, G. H., & Rayment, I. (1994) Biochemistry 33, 9333-9342]. The current crystallographic R-factor is 17.7% for all recorded data (92% complete) to 1.8 A resolution. The electron density map is unambiguous with respect to the positions and liganding of both magnesium ions and with respect to the stereochemistry of substrate/product binding. Both magnesium ions are complexed to functional groups of the substrate/product. The higher affinity Mg2+ coordinates to the carboxylate side chains of Asp 246, Glu 295, and Asp 320, both carboxylate oxygens of the substrate/product, and a water molecule. One of the carboxylate oxygens of the substrate/product also coordinates to the lower affinity Mg2+-thus forming a mu-carboxylato bridge. The other ligands of the second Mg2+ are a phosphoryl oxygen of the substrate/product, two water molecules, and the carbonyl and gamma-oxygens of Ser 39 from the active site loop. The intricate coordination of both magnesium ions to the carboxylate group suggests that both metal ions participate in stabilizing negative charge in the carbanion (aci-carboxylate) intermediate. The epsilon-amino group of Lys 345 is positioned to serve as the base in the forward reaction whereas the carboxylate side chain of Glu 211 is positioned to interact with the 3-OH of 2-PGA. The structure provides a candid view of the catalytic machinery of enolase.
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PMID:A carboxylate oxygen of the substrate bridges the magnesium ions at the active site of enolase: structure of the yeast enzyme complexed with the equilibrium mixture of 2-phosphoglycerate and phosphoenolpyruvate at 1.8 A resolution. 860 83


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