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rdf:type |
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lifeskim:mentions |
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pubmed:issue |
38
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pubmed:dateCreated |
1995-11-6
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pubmed:abstractText |
The pH dependence of kinetic parameters using natural and alternative reactants was determined in order to obtain information on the chemical mechanisms of the A and B isozymes of O-acetylserine sulfhydrylase (OASS) from Salmonella typhimurium. A general mechanism is proposed for OASS in which OAS binds with its alpha-amine unprotonated to carry out a nucleophilic attack on C4' of the protonated Schiff base and with the acetyl carbonyl hydrogen-bonded to a protonated enzyme group (or a water molecule), which aids in the beta-elimination of acetate. The enzyme lysine that was in Schiff base linkage with the active site pyridoxal 5'-phosphate deprotonates the alpha-carbon in the beta-elimination reaction, and a proton is likely released with the acetate product. Sulfide likely binds as HS- to undergo nucleophilic attack on the alpha-aminoacrylate intermediate, followed by protonation of the alpha-carbon by the enzyme lysine. In OASS-A, HS- is hydrogen-bonded to the enzyme group that assists in the beta-elimination of acetate, but this is not the case for OASS-B. The pH independent equilibrium constant for the first half-reaction of OASS-A is 1.6 x 10(-3), while the second half-reaction is practically irreversible.
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pubmed:language |
eng
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pubmed:journal |
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pubmed:citationSubset |
IM
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pubmed:chemical |
http://linkedlifedata.com/resource/pubmed/chemical/Acetates,
http://linkedlifedata.com/resource/pubmed/chemical/Cysteine Synthase,
http://linkedlifedata.com/resource/pubmed/chemical/Isoenzymes,
http://linkedlifedata.com/resource/pubmed/chemical/Lysine,
http://linkedlifedata.com/resource/pubmed/chemical/Nitrobenzoates,
http://linkedlifedata.com/resource/pubmed/chemical/O-acetylserine,
http://linkedlifedata.com/resource/pubmed/chemical/Pyridoxal Phosphate,
http://linkedlifedata.com/resource/pubmed/chemical/Schiff Bases,
http://linkedlifedata.com/resource/pubmed/chemical/Serine,
http://linkedlifedata.com/resource/pubmed/chemical/Sulfhydryl Compounds,
http://linkedlifedata.com/resource/pubmed/chemical/thionitrobenzoic acid
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pubmed:status |
MEDLINE
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pubmed:month |
Sep
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pubmed:issn |
0006-2960
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pubmed:author |
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pubmed:issnType |
Print
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pubmed:day |
26
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pubmed:volume |
34
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pubmed:owner |
NLM
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pubmed:authorsComplete |
Y
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pubmed:pagination |
12311-22
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pubmed:dateRevised |
2006-11-15
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pubmed:meshHeading |
pubmed-meshheading:7547974-Acetates,
pubmed-meshheading:7547974-Binding Sites,
pubmed-meshheading:7547974-Catalysis,
pubmed-meshheading:7547974-Cysteine Synthase,
pubmed-meshheading:7547974-Hydrogen-Ion Concentration,
pubmed-meshheading:7547974-Isoenzymes,
pubmed-meshheading:7547974-Kinetics,
pubmed-meshheading:7547974-Lysine,
pubmed-meshheading:7547974-Models, Chemical,
pubmed-meshheading:7547974-Nitrobenzoates,
pubmed-meshheading:7547974-Pyridoxal Phosphate,
pubmed-meshheading:7547974-Salmonella typhimurium,
pubmed-meshheading:7547974-Schiff Bases,
pubmed-meshheading:7547974-Serine,
pubmed-meshheading:7547974-Spectrophotometry,
pubmed-meshheading:7547974-Sulfhydryl Compounds,
pubmed-meshheading:7547974-Thermodynamics,
pubmed-meshheading:7547974-Titrimetry
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pubmed:year |
1995
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pubmed:articleTitle |
Acid-base chemical mechanism of O-acetylserine sulfhydrylases-A and -B from pH studies.
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pubmed:affiliation |
Department of Biochemistry and Molecular Biology, University of North Texas Health Sciences Center, Fort Worth 76107, USA.
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pubmed:publicationType |
Journal Article,
Comparative Study,
Research Support, U.S. Gov't, Non-P.H.S.,
Research Support, Non-U.S. Gov't
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