Linked Life Data

3778876

Source:http://linkedlifedata.com/resource/pubmed/id/3778876

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
19
pubmed:dateCreated
1987-1-9
pubmed:abstractText
The dependence on thiol pK of the second-order rate constant (kS) for reaction of thiolate anions with MMTS was shown to follow the Brønsted equation log kS = log G + beta pK with log G = 1.44 and 3.54 and beta = 0.635 and 0.309 for aryl and alkyl thiols, respectively. The reactivity toward MMTS of the protonated thiol group was found to be negligible in comparison to that of the thiolate anion. For 2-mercaptoethanol the reactivity toward MMTS of the protonated form of the thiol group was shown to be at least 5 X 10(9) smaller than that of the thiolate anion. The pH dependence of the second-order rate constant for reaction of the thiolate group of Cys-25 at the active site of papain was determined and shown to be consistent with the previously determined low pK for Cys-25 and its electrostatic interaction with His-159. The small dependence of the reactivity of Cys-25 on thiol pK (beta approximately 0.09) suggested that the charge-charge interactions that act through space to perturb the pK of the nucleophile at the active site of papain and perhaps other enzymes may serve to increase the fraction of nucleophile present in the reactive basic form without introducing the decrease in nucleophilic reactivity seen in model systems where pK's are lowered primarily by charge-dipole interactions.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Sep
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
23
pubmed:volume
25
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
5595-601
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1986
pubmed:articleTitle
Reactivity of small thiolate anions and cysteine-25 in papain toward methyl methanethiosulfonate.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S.