Linked Life Data

17029404

Source:http://linkedlifedata.com/resource/pubmed/id/17029404

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
41
pubmed:dateCreated
2006-10-10
pubmed:abstractText
Alpha-tocopherol, the most abundant form of vitamin E present in humans, is a noncompetitive inhibitor of glutathione S-transferase pi (GST pi), but its binding site had not been located. Tocopherol iodoacetate (TIA), a reactive analogue, produces a time-dependent inactivation of GST pi to a limit of 25% residual activity. The rate constant for inactivation, k(obs), exhibits a nonlinear dependence on reagent concentration, with K(I) = 19 microM and k(max) = 0.158 min(-)(1). Complete protection against inactivation is provided by tocopherol and tocopherol acetate, whereas glutathione derivatives, electrophilic substrate analogues, buffers, or nonsubstrate hydrophobic ligands have little effect on k(obs). These results indicate that TIA reacts as an affinity label of a distinguishable tocopherol binding site. Loss of activity occurs concomitant with incorporation of about 1 mol of reagent/mol of enzyme subunit when the enzyme is maximally inactivated. Isolation of the labeled peptide from the tryptic digest shows that Tyr(79) is the only enzymic amino acid modified. The Y79F, Y79S, and Y79A mutant enzymes were generated, expressed, and purified. Changing Tyr(79) to Ser or Ala, but not Phe, renders the enzyme insensitive to inhibition by either tocopherol or tocopherol acetate as demonstrated by increases of at least 49-fold in K(I) values as compared to the wild-type enzyme. These results and examination of the crystal structure of GST pi suggest that tocopherols bind at a novel site, where an aromatic residue at position 79 is essential for binding.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Oct
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
17
pubmed:volume
45
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
12491-9
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
2006
pubmed:articleTitle
Identification of tyrosine 79 in the tocopherol binding site of glutathione S-transferase pi.
pubmed:affiliation
Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA.
pubmed:publicationType
Journal Article, In Vitro, Research Support, N.I.H., Extramural