Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.1 (chymotrypsin)
 10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rat alpha 1-inhibitor-3 is a 180-kDa monomeric proteinase inhibitor found in high concentration in rat plasma. By several criteria it has been shown to be a member of the family of alpha-macroglobulin proteinase inhibitors often exemplified by the tetrameric human alpha 2-macroglobulin. We have used limited proteolysis of rat alpha 1-inhibitor-3 to probe the domain structure of this family of proteins. Proteinases of different specificities, including trypsin, chymotrypsin, thermolysin, and Staphylococcus aureus V8 proteinase, were employed and a common fragmentation pattern was observed when the reaction products were examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. These fragments were electrotransferred to polyvinylidene difluoride membranes and subjected to NH2-terminal amino acid sequence analysis in order to position them within the context of the primary structure. The fragmentation pattern may define the domain structure of alpha 1-inhibitor-3 and serve as a model for the domain organization of the family of alpha-macroglobulin proteinase inhibitors.
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PMID:Limited proteolysis of the alpha-macroglobulin rat alpha 1-inhibitor-3. Implications for a domain structure. 171 Feb 22

The molecular basis for binding of alpha-macroglobulin-proteinase complexes to the human two-chain 500/85-kDa (alpha/beta) alpha 2-macroglobulin (alpha 2M) receptor (alpha 2MR)/low density lipoprotein receptor-related protein was analyzed. Ligand blotting experiments showed that a 40-kDa protein, present in the affinity-purified alpha 2MR preparation, is bound to the alpha 2MR alpha-chain and released by heparin. Removal of the 40-kDa protein resulted in a 3-5-fold increase in binding of alpha 2M-trypsin. Nitrocellulose-immobilized pure two-chain alpha 2MR was incubated with human alpha 2M-trypsin, containing four identical subunits, and two monovalent ligands: rat alpha 1-inhibitor-3-chymotrypsin and the 18-kDa receptor binding fragment of the alpha 2M subunit. Binding of alpha 2M-trypsin to the alpha-chain of immobilized alpha 2MR was composed of a high (Kd = 40 pM at 4 degrees C) and a low (Kd = 2 nM) affinity component. alpha 1-Inhibitor-3-chymotrypsin bound to the same sites but with one component (Kd = 0.4 nM). Competition-inhibition experiments and dissociation experiments, using ligands with different valences, as well as experiments with alpha 2MR immobilized at different densities, led to the following model. The low (Kd = 2 nM) affinity of alpha 2M-proteinase is prevalent when only one of the four domains binds to alpha 2MR, i.e. when the receptor density is low or when neighboring receptors are occupied. The high (Kd = 40 pM) affinity is achieved by binding of at least two domains to adjacent receptors.
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PMID:Analysis of ligand recognition by the purified alpha 2-macroglobulin receptor (low density lipoprotein receptor-related protein). Evidence that high affinity of alpha 2-macroglobulin-proteinase complex is achieved by binding to adjacent receptors. 171 12

The primary sequence of the affinity purified chymotrypsin inhibitor, WBCI, isolated from the albumin fraction of Psophocarpus tetragonolobus (L.) DC cv. UPS-122 seed was determined. The inhibitor consisted of a single polypeptide chain of 183 amino acids (Mr 20285) and the four half-cystine residues in the molecule formed two intramolecular disulfide bridges equivalent to those in other Kunitz-type seed inhibitors. The sequence of this chymotrypsin inhibitor was identical to that of chymotrypsin inhibitor-3 from cultivar UPS-31 and it showed about 50% sequence similarity to the winged bean acidic (WBTI-2, pI 5.1) and basic (WBTI-1, pI 8.9) trypsin inhibitors. Sequence similarities to other Kunitz-type seed inhibitors are discussed.
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PMID:Amino acid sequence and disulfide bridges of affinity purified Kunitz-type chymotrypsin inhibitor from winged bean seed (Psophocarpus tetragonolobus (L.) DC). 207 11

Receptors for alpha 2-macroglobulin-proteinase complexes have been characterized in rat and human liver membranes. The affinity for binding of 125I-labelled alpha 2-macroglobulin.trypsin to rat liver membranes was markedly pH-dependent in the physiological range with maximum binding at pH 7.8-9.0. The half-time for association was about 5 min at 37 degrees C in contrast to about 5 h at 4 degrees C. The half-saturation constant was about 100 pM at 4 degrees C and 1 nM at 37 degrees C (pH 7.8). The binding capacity was approx. 300 pmol per g protein for rat liver membranes and about 100 pmol per g for human membranes. Radiation inactivation studies showed a target size of 466 +/- 71 kDa (S.D., n = 7) for alpha 2-macroglobulin.trypsin binding activity. Affinity cross-linking to rat and human membranes of 125I-labelled rat alpha 1-inhibitor-3.chymotrypsin, a 210 kDa analogue which binds to the alpha 2-macroglobulin receptors in hepatocytes (Gliemann, J. and Sottrup-Jensen, L. (1987) FEBS Lett. 221, 55-60), followed by SDS-polyacrylamide gel electrophoresis, revealed radioactivity in a band not distinguishable from that of cross-linked alpha 2-macroglobulin (720 kDa). This radioactivity was absent when membranes with bound 125I-alpha 1-inhibitor-3 complex were treated with EDTA before cross-linking and when incubation and cross-linking were carried out in the presence of a saturating concentration of unlabelled complex. The saturable binding activity was maintained when membranes were solubilized in the detergent 3-[(3-cholamidopropyl)dimethylammonio]propane sulfonate (CHAPS) and the size of the receptor as estimated by cross-linking experiments was shown to be similar to that determined in the membranes. It is concluded that liver membranes contain high concentrations of an approx. 400-500 kDa alpha 2-macroglobulin receptor soluble in CHAPS. The soluble preparation should provide a suitable material for purification and further characterization of the receptor.
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PMID:Characterization, size estimation and solubilization of alpha-macroglobulin complex receptors in liver membranes. 246 80