Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.17 (lysozyme)
 21,489 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

S-mercuric-N-dansylcysteine was investigated as a potential probe of protein sulphydryl groups using bovine serum albumin, S-carboxymethyl-bovine serum albumin, lysozyme, and partially reduced lysozyme as test proteins. Criteria used to assess covalent binding through mercury-bridged mercaptide linkages include a finite reaction time (minutes to hours), abolition of the characteristic fluorescence spectrum following addition of a reducing agent, and failure to separate probe and protein after chromatography or electrophoresis. By these criteria, both Torpedo californica acetylcholinesterase and human serum cholinesterase (butyrylcholinesterase) contain four free sulphydryl groups per tetrameric enzyme molecule whereas Electrophorus electricus acetylcholinesterase has none. Labeled acetylcholinesterase and butyrylcholinesterase remain active and responsive to the inactivator Zn2+. Zn2+ promotes an increase in the fluorescence of bound S-mercuric-N-dansylcysteine, whereas activators such as Mg2+ or gallamine promote a decrease, suggesting that the label may be a useful probe of ligand-induced conformational changes. With T. californica acetylcholinesterase, but not with human serum cholinesterase, Zn2+ also promotes access to two additional groups that are reactive towards the sulphydryl reagent.
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PMID:The reaction of S-mercuric-N-dansylcysteine with acetylcholinesterase and butyrylcholinesterase. 278 87

The nicotinic receptor is highly phosphorylated on tyrosine residues both in vivo and in vitro. Tyrosine phosphorylation has been shown to regulate the functional properties of the receptor. We have purified a protein tyrosine phosphatase from the electric organ of Torpedo californica that dephosphorylates the nicotinic receptor. The unique biochemical properties of the purified enzyme suggest that it may be a novel phosphotyrosine protein phosphatase. In this report, substrate specificity of the protein purified from T. californica was characterized using four different tyrosine-phosphorylated substrate proteins. In addition to the nicotinic receptor, the Torpedo phosphatase dephosphorylated insulin receptor and Reduced Carboxamidomethylated and Meleylated lysozyme (RCM lysozyme), however, at a rate much slower than for the nicotinic receptor. In contrast, it appeared to have no effect on the phosphotyrosine level of pp15, a fatty acid binding protein (O-phospho-tyr19-422/aP2) phosphorylated by insulin receptor kinase in 3T3-L1 adipocytes. Interestingly, a protein tyrosine phosphatase (HA1) purified from adipocyte dephosphorylated both nicotinic receptor and pp15 at a similar rate. These results suggest that the Torpedo protein tyrosine phosphatase is relatively specific for the nicotinic receptor.
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PMID:Characterization of substrate specificity of the protein tyrosine phosphatase purified from the electric organ of Torpedo californica. 789 79