Linked Life Data

10521455

Source:http://linkedlifedata.com/resource/pubmed/id/10521455

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
43
pubmed:dateCreated
1999-11-23
pubmed:databankReference
pubmed:abstractText
The initial reaction of tetrapyrrole formation in archaea is catalyzed by a NADPH-dependent glutamyl-tRNA reductase (GluTR). The hemA gene encoding GluTR was cloned from the extremely thermophilic archaeon Methanopyrus kandleri and overexpressed in Escherichia coli. Purified recombinant GluTR is a tetrameric enzyme with a native M(r) = 190,000 +/- 10,000. Using a newly established enzyme assay, a specific activity of 0.75 nmol h(-1) mg(-1) at 56 degrees C with E. coli glutamyl-tRNA as substrate was measured. A temperature optimum of 90 degrees C and a pH optimum of 8.1 were determined. Neither heme cofactor, nor flavin, nor metal ions were required for GluTR catalysis. Heavy metal compounds, Zn(2+), and heme inhibited the enzyme. GluTR inhibition by the newly synthesized inhibitor glutamycin, whose structure is similar to the 3' end of the glutamyl-tRNA substrate, revealed the importance of an intact chemical bond between glutamate and tRNA(Glu) for substrate recognition. The absolute requirement for NADPH in the reaction of GluTR was demonstrated using four NADPH analogues. Chemical modification and site-directed mutagenesis studies indicated that a single cysteinyl residue and a single histidinyl residue were important for catalysis. It was concluded that during GluTR catalysis the highly reactive sulfhydryl group of Cys-48 acts as a nucleophile attacking the alpha-carbonyl group of tRNA-bound glutamate with the formation of an enzyme-localized thioester intermediate and the concomitant release of tRNA(Glu). In the presence of NADPH, direct hydride transfer to enzyme-bound glutamate, possibly facilitated by His-84, leads to glutamate-1-semialdehyde formation. In the absence of NADPH, a newly discovered esterase activity of GluTR hydrolyzes the highly reactive thioester of tRNA(Glu) to release glutamate.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Oct
pubmed:issn
0021-9258
pubmed:author
pubmed:issnType
Print
pubmed:day
22
pubmed:volume
274
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
30679-85
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
1999
pubmed:articleTitle
Methanopyrus kandleri glutamyl-tRNA reductase.
pubmed:affiliation
Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität Freiburg, D-79104 Freiburg im Breisgau, Germany.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't