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)

A 32,000-dalton protein (p32) located in avian retrovirus cores was immunoprecipitated from [35S]methionine-labeled avian myeloblastosis virus (AMV) propagated in cultured chicken embryo fibroblast cells by an antiserum preparation (sarc III) derived from tumor-bearing hamsters injected with cloned and passaged cells from an avian sarcoma virus-induced primary hamster tumor. Since sarc III serum apparently contained antibodies only to virus-coded proteins and not to chicken cellular proteins, the immunoprecipitation of p32 from AMV by sarc III serum strongly suggested that p32 is virus coded. The origin of p32 was more definitively established by demonstrating the existence of a structural relationship between p32 and the AMV DNA polymerase. AMV p32 cross-reacted with the beta polypeptide of AMV alphabeta DNA polymerase in radioimmunoprecipitation and radioimmunoprecipitation inhibition assays, indicating that p32 and beta share common antigenic determinants. This relationship was clarified by sodium do-decyl sulfate-polyacrylamide gel electrophoretic analysis of the peptides generated by limited proteolysis of 125I-labeled AMV DNA polymerase polypeptides and of 125I-labeled AMV p32 by chymotrypsin or Staphylococcus aureus V-8 protease. The peptides which appeared during proteolytic digestion of p32 were a subset of those produced by digestion of the beta polypeptide; however, p32 had no discernible peptides in common with the alpha polypeptide. Further, all of the peptides produced by limited proteolysis of beta were present in the digests of either p32 or alpha. Our findings suggest that p32 is apparently derived by cleavage of the beta polypeptide of AMV DNA polymerase, presumably at a site near or identical to that at which alpha is generated from beta by proteolytic cleavage.
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PMID:Virus-coded origin of a 32,000-dalton protein from avian retrovirus cores: structural relatedness of p32 and the beta polypeptide of the avian retrovirus DNA polymerase. 8 16

Purified phosphofructokinase 1 from baker's yeast (Saccharomyces cerevisiae) was subjected to proteolysis by thermolysin, endoproteinase lys-C, trypsin and chymotrypsin under defined solvent conditions. In the absence of substrates and allosteric effectors, the catalytic activity of phosphofructokinase rapidly disappeared in the presence of each proteolytic enzyme. The presence of a saturating concentration of ATP protected phosphofructokinase activity from proteolytic inactivation while the collective presence of fructose 6-phosphate, AMP and fructose 2,6-bisphosphate provided transient activation during proteolysis. Changes in the quaternary structure of phosphofructokinase resulting from proteolysis were estimated by high performance size exclusion chromatography while changes in the primary sequence of the individual alpha and beta polypeptide chains were estimated by polyacrylamide-gel electrophoresis in sodium dodecylsulfate. The site(s) of proteolytic cleavage were identified by N-terminal sequence analysis of resolved electrophoretic components. The presence of ATP protects phosphofructokinase from thermolysin proteolysis, while the collective presence of fructose 6-phosphate, AMP and fructose 2,6-bisphosphate restricts proteolysis to one site in each polypeptide chain involving the peptide bonds preceding Leu199 in the alpha chain and Leu192 in the beta chain. The truncated phosphofructokinase retains its octameric structure. The presence of ATP largely restricts endoproteinase lys-C proteolysis to a single site in the alpha chain involving the peptide bond preceding Val914. This cleavage results in the dissociation of the octameric form of phosphofructokinase into two tetramers. The presence of ATP restricts both trypsin and chymotrypsin proteolysis to the N-terminal and C-terminal regions described above, resulting in the preferential stabilization of the tetrameric form of phosphofructokinase. It would appear that the first 200 and last 80 residues which are unique to the sequence of the yeast phosphofructokinase are not directly involved in catalysis or its allosteric regulation. However, the last 80 residues of the alpha polypeptide chain do appear to stabilize an octameric structure which is unique to yeast phosphofructokinase.
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PMID:Limited proteolysis of yeast phosphofructokinase. Sequence locations of cleavage sites created by the actions of different proteinases. 822 96