Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.4 (trypsin)
42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have studied the surface proteins of normal and transformed chick cells using four-labelling techniques with different specificities, (a) lactoperoxidase catalysed iodination (b) galactose oxidase/B3H4 (c) pyridoxal phosphate/B3H4 and (d) periodate/B3H4. All methods labelled a large external transformation-sensitive (LETS) protein, in agreement with previous studies. In addition, using galactose oxidase and periodate labelling techniques, we present evidence which suggests that the transformed cell surface glycoproteins are more sialylated. The LETS protein was also labelled with (14C) glucosamine and after trypsinization a small band of identical molecular weight to LETS remained, possibly representing an internal pool of the protein. In contrast LETS protein labelled with (3H) fucose was completely removed by trypsin, suggesting that the internal pool of the protein is incompletely glycosylated. Evidence is also presented to show that although the level of the protein is drastically reduced at the transformed cell surface, it is still synthesised and shed into the medium.
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PMID:Cell surface and metabolic labelling of the proteins of normal and transformed chicken cells. 17 96

Transfer of folate compounds was studied in human erythrocytes. At steady state, the measured distribution ratio of 5-CH3-H4-folate in erythrocyte suspensions exceeded the ratio predicted from the chloride distribution ratio by a factor of 1.58, suggesting that human erythrocytes concentrate folate. Because folate compounds are anionic at physiologic pH, we investigated the possibility that transport occurs via the inorganic anion channel associated with the predominant integral membrane protein, band 3. Erythrocyte uptake of 5-CH3-H4-folate was decreased (60% to 80%) by several known inhibitors of anion transport--pyridoxal phosphate, dipyridamole, phlorizin, and SITS. However, unlike the inorganic anion transfer system, 5-CH3-H4-folate uptake was only slightly decreased by DIDS; was reduced 50% to 70% by the sulfhydryl reagents NEM, PMB, and pCMBS; and was not affected by the proteolytic enzymes trypsin, chymotrypsin, and pronase. These studies suggest that folate compounds are transported by a specialized carrier system, independent of the inorganic anion channel, which contains sulfhydryl and amino groups. In contrast to 5-CH3-H4-folate transfer, uptake of pteroylglutamic acid was either unaffected or somewhat increased by these membrane modifications. This result indicates that the human erythrocyte transports the reduced and oxidized forms of the vitamin by entirely separate mechanisms.
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PMID:Evidence for transfer of folate compounds by a specialized erythrocyte membrane system. 22 54

Phosphorylases a and b were inactivated very rapidly by a neutral, trypsin-like protease from rat intestinal muscle. With 32P-phosphorylase a as substrate, it was shown that the initial event in the inactivation was the release of a small, phosphopeptide from the N-terminus of the enzyme, leaving the original 100,000 subunit form virtually unchanged. Subsequent proteolysis was very limited, producing 85, 70 and 65,000 mol. wt. derivatives. The effects of several allosteric modulators of phosphorylase on the rates of inactivation of the two enzymes were studied. Removal of the pyridoxal phosphate cofactor from phosphorylase increased the susceptibility of the b form by three fold while the a form was unaffected. By comparison of these effects with those obtained from digestion with trypsin and chymotrypsin, it is concluded that the intestinal muscle protease has a markedly enhanced ability for inactivating enzymes in their native conformation. Assuming that this property is reflected in vivo, a possible role such neutral proteases in initiating protein degradation is advanced.
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PMID:The susceptibility of glycogen phosphorylase to inactivation by endogenous and exogenous proteases. 61 10

"Group-specific" protease (GSP) is a serine protease, obtained from rat small intestine, which preferentially inactivates the apo forms of certain pyridoxal phosphate requiring enzymes. The enzyme contains 224 amino acid residues in a single polypeptide chain and three disulfide bonds. In the present work the covalent structure has been determined and its homologous relationship to those of chymotrypsin, trypsin, and elastase has been established (approximately 33% identity with each). The residues forming the "charge-relay" system of the active site of chymotrypsin (His-57, Asp-102, and Ser-195) are found in corresponding regions in GSP, whereas an alanyl residue at position 176 of GSP corresponds to a residue which participates in the primary substrate binding site in serine proteases (Asp-177 in trypsin; Ser-189 in chymotrypsin). Three disulfide bonds in GSP occur in similar positions in chymotrypsin, trypsin, and elastase. However, GSP lacks a disulfide bond which is present in all known serine proteases (linking Cys-191 to Cys-220 in chymotrypsin). In view of the close proximity of this bond to both the primary and the antiparallel binding sites of various serine proteases, it is likely that its absence in GSP is related to the substrate specificity of this enzyme. It is concluded that GSP diverged from a common ancestor preceding chymotrypsin but following trypsin.
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PMID:Covalent structure of a group-specific protease from rat small intestine. Appendix: crystallographic data for a group specific protease from rat intestine. 62 33

1. Phosphorylase b was inactivated three times more rapidly than phosphorylase a by a neutral, trypsin-like proteinase from rat intestinal muscle. Digestion of phosphorylase a produced a modified form which was deactivated by AMP. Removal of the pyridoxal phosphate cofactor increased the rate of inactivation of the b form by about 3-fold but the subceptibility of apophosphorylase a was no different from the holo form. 2. The extent of proteolysis of both holoenzyme forms, as guaged by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, was limited and similar digestion patterns were obtained in both cases. 3. With (32)P-labelled phosphorylase a as substrate, the initial event in the inactivation was the release of a trichloroacetic acid-soluble peptide from the N-terminus of the enzyme, leaving the original 100000 subunit form essentially unchanged. Subsequent proteolysis was restricted, producing derivatives of mol.wt. 85000, 70000 and 65000, none of which contained any radioactive label. 4. By treatment of inactivated phosphorylase b with carboxypeptidase B, it was shown that the intestinal muscle proteinase had cleaved approximately 3 -Lys-X and 3 -Arg-X bonds in the polypeptide. 5. The protective effects of various allosteric modulators of phosphorylase on the inactivation of the a and b forms were generally in agreement with the known roles of the modifiers. Glucose increased the susceptibility of phosphorylase a. 6. Inactivation of phosphorylase b by trypsin and chymotrypsin also resulted in limited proteolysis but, in both cases, the digestion patterns obtained on sodium dodecyl sulphate/polyacrylamide gels were different from each other and from the pattern obtained with the intestinal muscle proteinase. 7. Inactivation of phosphorylase b by the muscle proteinase is about 100 times more rapid than the effects produced by trypsin or chymotrypsin when the activities are compared on an equimolar basis. 8. Consideration is given to regulation of the rate of enzyme degradation intracellularly by modulation of the conformation and susceptibility of the enzyme via factors such as covalent modification, allosteric ligands and state of aggregation.
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PMID:The susceptibility of muscle phosphorylases a and b to digestion by a neutral proteinase from rat intestinal muscle. Comparison with the effects produced by pancreatic trypsin and chymotrypsin. 73 88

O-Acetylserine-O-acetylhomoserine sulfhydrylase [EC class 4.2.99], catalyzing the sulfhydrylation of both O-acetyl-L-serine (OAS) and O-acetyl-L-homoserine (OAH) (O-acetyl-L-serine(O-acetyl-L-homoserine) + H2S leads to L-cysteine (L-homocysteine) + acetate), was extracted and purified from bakers' yeast by an improved method. The purified enzyme was shown to be homogeneous on polyacrylamide gel electrophoresis both in the absence and presence of sodium dodecylsulfate and by ultracentrifugal analysis. The apo-enzyme was protected by pyridoxal phosphate (PALP) from inactivation by heat, urea, and trypsin [EC 3.4.21.4], suggesting that the binding of PALP to the apo-enzyme rendered the conformation of the protein more stable. The holo-enzyme showed absorption peaks at 420 and 330 nm due to bound PALP, in addition to a peak at 280 nm. Upon reduction with borohydride, the 420-nm peak disappeared and an increase in the 330-nm peak occurred concomitant with loss of the catalytic activity. Lysine appeared to be the pyridoxal binding site, based on identification of pyridoxyl-lysine in the hydrolyzate of the holo-enzyme. It was shown by both spectral and chemical determinations that 4 moles of PALP could bind to 200,000 g of apo-protein. The apo-enzyme showed a lower association constant with PALP than some other enzymes. Pyridoxal inhibited the activity competitively with respect to PALP. Based on these findings, it appears that the reaction mechanism of this enzyme is similar to those of other pyridoxal enzymes.
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PMID:O-Acetylserine and O-acetylhomoserine sulfhydrylase of yeast. Further purification and characterization as a pyridoxal enzyme. 79 6

1. Specific proteases which inactivate the apo-proteins of many pyridoxal enzymes were found in skeletal muscle, liver and small intestine of rats. The protease from these three organs were purified and their properties were compared. 2. The purified proteases from liver and skeletal muscle appeared homogeneous on acrylamide gel electrophoresis. Two different proteases were separated from small intestine. A homogeneous, crystalline enzyme was obtained from the muscle layer while enzyme from the mucosa was partially purified. 3. They showed substrate specificity for pyridoxal enzymes. Their pH optima were in an alkaline region. They showed activity with the substrate of chymotrypsin, N-acetyl-L-tyrosine ethyl ester, but not with that of trypsin, p-toluenesulfonyl-L-arginine ethyl ester. They were inhibited by pyridoxal phosphate or pyridoxamine phosphate and seryl residues were involved in their active center. 4. The four enzymes differed in the following characters: (a) molecular weights; (b) patterns of elution from a CM-Sephadex column; (c) rates of inactivation of substrate enzymes; (d) rates of cleavage of N-acetyl-L-tyrosine ethyl ester; (e) reactivities with antiserum against the enzyme from the muscle layer of small intestine; (f) specific activities. 5. The amino acid composition and effect of chemical modifications of the crystalline enzyme from the muscle layer of small intestine were examined to elucidate its active sites and mode of action. Serine and histidine residues were found to be essential for protease activity. A tyrosine residue was also necessary for activity. Modifications of its sulfhydryl group, amino residues and carboxyl group had no effect on its activity.
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PMID:Studies on new intracellular proteases in various organs of rat. 1. Purification and comparison of their properties. 116 13

This study explores the catalytic and allosteric roles of a flexible loop in tryptophan synthase. Trypsin is known to cleave the tryptophan synthase alpha 2 beta 2 complex in an alpha subunit loop at Arg-188. Cleavage yields an active "nicked" alpha 2 beta 2 derivative. The new results provide evidence that the alpha subunit loop serves two important roles: substrate binding and communicating the effects of substrate binding to the beta subunit. A role for the loop in substrate binding is supported by our finding that addition of a substrate analogue of the alpha subunit, alpha-glycerol 3-phosphate, decreases the rate of cleavage by trypsin. An allosteric role for the loop is supported by the finding although the native alpha 2 beta 2 complex is strongly inhibited by alpha-glycerol 3-phosphate, the nicked alpha 2 beta 2 complex is desensitized to this inhibition. The time course of proteolysis in the presence and absence of alpha-glycerol 3-phosphate is followed by sodium dodecyl sulfate-gel electrophoresis and by assays of activity in the presence and absence of alpha-glycerol 3-phosphate. We use spectroscopic measurements of the pyridoxal phosphate-L-tryptophan intermediates at the active site of the beta subunit to determine the affinity of the native and nicked enzymes for L-tryptophan and alpha-glycerol 3-phosphate. Although cleavage alters the equilibrium distribution of intermediates and reduces the affinity for alpha-glycerol 3-phosphate, it has little effect on the affinity for amino acids bound to the beta subunit. We conclude that the loop in the alpha subunit is important for ligand binding and for communicating the effects of ligand binding from the alpha subunit to the beta subunit in the alpha 2 beta 2 complex.
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PMID:The tryptophan synthase alpha 2 beta 2 complex. Cleavage of a flexible loop in the alpha subunit alters allosteric properties. 190 55

The pyridoxal phosphate (PLP)-dependent 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (S-adenosyl-L-methionine methylthioadenosine-lyase, EC 4.4.1.14), the key enzyme in ethylene biosynthesis, is inactivated by its substrate S-adenosylmethionine (AdoMet). Apple ACC synthase was purified with an immunoaffinity gel, and its active site was probed with NaB3H4 or Ado[14C]Met. HPLC separation of the trypsin digest yielded a single radioactive peptide. Peptide sequencing of both 3H- and 14C-labeled peptides revealed a common dodecapeptide of Ser-Leu-Ser-Xaa-Asp-Leu-Gly-Leu-Pro-Gly-Phe-Arg, where Xaa was the modified, radioactive residue in each case. Acid hydrolysis of the 3H-labeled enzyme released radioactive N-pyridoxyllysine, indicating that the active-site peptide contained lysine at position 4. Mass spectrometry of the 14C-labeled peptide indicated a protonated molecular ion at m/z 1390.6, from which the mass of Xaa was calculated to be 229, a number that is equivalent to the mass of a lysine residue alkylated by the 2-aminobutyrate portion of AdoMet, as we previously proposed. These results indicate that the same active-site lysine binds the PLP and convalently links to the 2-aminobutyrate portion of AdoMet during inactivation. The active site of tomato ACC synthase was probed in the same manner with Ado[14C]Met. Sequencing of the tomato active-site peptide revealed two highly conserved dodecapeptides; the minor peptide possessed a sequence identical to that of the apple enzyme, whereas the major peptide differed from the minor peptide in that methionine replaced leucine at position 6.
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PMID:Characterization and sequencing of the active site of 1-aminocyclopropane-1-carboxylate synthase. 212 49

The dispositions with respect to the plane of the membrane of lysine-905 in the internal sequence -EQRKIVE- and of lysine-1012 in the carboxy-terminal sequence -RRPGGWVEKETYY of the alpha-polypeptide of sodium and potassium ion activated adenosinetriphosphatase have been determined. These lysines are found in peptides released from the intact alpha-polypeptide by the extracellular protease from Staphylococcus aureus strain V8 and by trypsin, respectively. Synthetic peptides containing terminal sequences of these were used to prepare polyclonal antibodies, which were then used to prepare immunoadsorbents directed against the respective peptides. Sealed, right-side-out membrane vesicles containing native (Na+ + K+)-ATPase were labeled with pyridoxal phosphate and sodium [3H]borohydride in the absence or presence of saponin. The labeled alpha-polypeptide was isolated from these vesicles and digested with appropriate proteases. The incorporation of radioactivity into the peptides binding to the immunoadsorbent directed against the sequence pyrERXIVE increased 3-fold in the presence of saponin as a result of the increased accessibility of this portion of the protein to the reagent when the vesicles were breached by saponin; hence, this sequence is located on the cytoplasmic face of the membrane. It was inferred that the carboxy-terminal sequence -KETYY is on the extracytoplasmic face since the incorporation of radioactivity into peptides binding to the immunoadsorbent directed against the sequence -ETYY did not change when the vesicles were breached with saponin.
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PMID:Topological disposition of the sequences -QRKIVE- and -KETYY in native (Na+ + K+)-ATPase. 215 94


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