Linked Life Data

16606627

Source:http://linkedlifedata.com/resource/pubmed/id/16606627

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
23
pubmed:dateCreated
2006-6-5
pubmed:abstractText
During porphyrin biosynthesis the oxygen-independent coproporphyrinogen III oxidase (HemN) catalyzes the oxidative decarboxylation of the propionate side chains of rings A and B of coproporphyrinogen III to form protoporphyrinogen IX. The enzyme utilizes a 5'-deoxyadenosyl radical to initiate the decarboxylation reaction, and it has been proposed that this occurs by stereo-specific abstraction of the pro-S-hydrogen atom at the beta-position of the propionate side chains leading to a substrate radical. Here we provide EPR-spectroscopic evidence for intermediacy of the latter radical by observation of an organic radical EPR signal in reduced HemN upon addition of S-adenosyl-L-methionine and the substrate coproporphyrinogen III. This signal (g(av) = 2.0029) shows a complex pattern of well resolved hyperfine splittings from at least five different hydrogen atoms. The radical was characterized using regiospecifically labeled (deuterium or 15N) coproporphyrinogen III molecules. They had been generated from a multienzyme mixture and served as efficient substrates. Reaction of HemN with coproporphyrinogen III, perdeuterated except for the methyl groups, led to the complete loss of resolved proton hyperfine splittings. Substrates in which the hydrogens at both alpha- and beta-positions, or only at the beta-positions of the propionate side chains, or those of the methylene bridges, were deuterated showed that there is coupling with hydrogens at the alpha-, beta-, and methylene bridge positions. Deuterium or 15N labeling of the pyrrole nitrogens without labeling the side chains only led to a slight sharpening of the radical signal. Together, these observations clearly identified the radical signal as substrate-derived and indicated that, upon abstraction of the pro-S-hydrogen atom at the beta-position of the propionate side chain by the 5'-deoxyadenosyl radical, a comparatively stable delocalized substrate radical intermediate is formed in the absence of electron acceptors. The observed hyperfine constants and g values show that this coproporphyrinogenyl radical is allylic and encompasses carbon atoms 3', 3, and 4.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jun
pubmed:issn
0021-9258
pubmed:author
pubmed:issnType
Print
pubmed:day
9
pubmed:volume
281
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
15727-34
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
2006
pubmed:articleTitle
The substrate radical of Escherichia coli oxygen-independent coproporphyrinogen III oxidase HemN.
pubmed:affiliation
Institute of Microbiology, Technical University Braunschweig, Spielmannstrasse 7, 38106 Braunschweig, Germany. gunhild.layer@cea.fr
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't