Linked Life Data

3907704

Source:http://linkedlifedata.com/resource/pubmed/id/3907704

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
24
pubmed:dateCreated
1986-2-13
pubmed:abstractText
The serine residue in the active center of atropinesterase (AtrE), alpha-chymotrypsin (Chymo), and subtilisin A (Sub) and in alpha-chymotrypsinogen (Chymogen) was labeled with a diisopropylphosphoryl (DP) group. The labeled proteins were studied in buffered aqueous solution under various native and denaturing conditions with 31P NMR before and after being subjected to "ageing", a process leading to conversion of the DP group into a monoisopropylphosphoryl (MP) group. Besides, the model compounds Gly-Ser(DP), Gly-Glu-Ser(DP)-Gly-OEt, and diisopropyl hydrogen phosphate were investigated under similar conditions and in other solvents with different hydrogen-bonding capacity. Mass spectrometry was used to analyze products resulting from ageing in the presence of H2(18)O. The 31P chemical shift of the DP proteins increases according to a simple titration curve upon lowering the pH from 9.0 to 5.0. This is ascribed to protonation of a particular histidine residue in the active center that interacts with a nearby isopropoxy group by hydrogen bonding with the ester oxygen. In DP-AtrE, hydrogen bonding at the phosphoryl oxygen dominates the interaction between substituent and protein; in the other DP proteins, nonbonding interactions become more dominant in the order Chymogen less than Chymo less than Sub. DP-AtrE, DP-Chymo, and DP-Sub age according to first-order kinetics. The pH dependence of the reaction rate constant ka indicates that ageing is catalyzed by the protonated histidine, which is responsible for the increase in chemical shift. The direct interaction between the phosphoryl group and the histidine is lost upon ageing whereas there is an increase in the nonbonding interaction of the remaining isopropyl group with the protein in the order Chymo less than Sub less than AtrE. The maximum value of ka when the histidine is fully protonated (kam) increases in the same order. Ageing of the DP enzymes occurs exclusively by C-O fission, yielding 2-propanol and propene. Since the amount of 2-propanol decreased and that of propene increased in the order Chymo to Sub to AtrE, the increase in kam has been interpreted as a shift in character of ageing from mainly SN2 for Chymo to considerably SN1 for AtrE and Sub. This has been attributed to preferential stabilization of the SN1 transition state by an interplay of hydrogen-bonding and nonbonding interactions between the phosphoryl group and the protein.(ABSTRACT TRUNCATED AT 400 WORDS)
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Nov
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
19
pubmed:volume
24
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
6894-903
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
1985
pubmed:articleTitle
P NMR and mass spectrometry of atropinesterase and some serine proteases phosphorylated with a transition-state analogue.
pubmed:publicationType
Journal Article