Linked Life Data

2656672

Source:http://linkedlifedata.com/resource/pubmed/id/2656672

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
14
pubmed:dateCreated
1989-6-30
pubmed:abstractText
Macroscopic pKa values associated with the influence of pH on the visible spectrum of 2-electron reduced pig heart lipoamide dehydrogenase and yeast glutathione reductase have been determined by monitoring changes in the principal flavin band near 460 nm and the charge transfer band at 540 nm. The ionization of at least three active site amino acid side chains can influence the spectra over the range of pH studied: the two nascent thiols (interchange thiol and electron transfer thiol) and the histidine residue which acts as the base catalyst in lipoamide dehydrogenase and the acid catalyst in glutathione reductase thiol-disulfide interchange reactions. These systems are analogous to, but more complex than, those in glyceraldehyde-3-phosphate dehydrogenase and papain where a single thiol and a histidine residue in a relatively apolar milieu form a thiolate-imidazolium ion pair which is favored over the thiol-imidazole prototropic tautomer. In an effort to more nearly mimic the papain titrations, the macroscopic pKa values were determined on reduced glutathione reductase which had been monoalkylated with iodoacetamide under conditions known to favor the reaction of the interchange thiol by at least 10 to 1 (Arscott, L. D., Thorpe, C., and Williams, C. H., Jr. (1981) Biochemistry 20, 1513-1520). Like papain and glyceraldehyde-3-phosphate dehydrogenase, alkylated glutathione reductase showed two macroscopic pKa values, at pH 3.7 and pH 9.1, and by analogy, these were associated primarily with the thiol and the imidazole, respectively. Results with the native enzymes depended on the wavelength monitored. Glutathione reductase had pKa values at 4.8, 7.1, and 9.2 when monitored at 540 nm and 5.1 and 8.2 when monitored at 462 nm. Lipoamide dehydrogenase had pKa values at 4.4 and 8.7 when monitored at 529 nm and 3.9, 7.0, and 9.3 when monitored at 455 nm.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
May
pubmed:issn
0021-9258
pubmed:author
pubmed:issnType
Print
pubmed:day
15
pubmed:volume
264
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
8033-8
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1989
pubmed:articleTitle
Titration studies on the active sites of pig heart lipoamide dehydrogenase and yeast glutathione reductase as monitored by the charge transfer absorbance.
pubmed:affiliation
Veterans Administration Medical Center, Ann Arbor, Michigan 48105.
pubmed:publicationType
Journal Article, Comparative Study, Research Support, U.S. Gov't, P.H.S., Research Support, U.S. Gov't, Non-P.H.S.