Linked Life Data

8476750

Source:http://linkedlifedata.com/resource/pubmed/id/8476750

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
4-6
pubmed:dateCreated
1993-5-26
pubmed:abstractText
Aromatase is a microsomal cytochrome P450 that converts androgens to estrogens by three sequential oxidations. The isolation of the 19-hydroxy and 19-oxo androgens suggests that the first two oxidations occur at the C19 carbon. However, the mechanism of the third oxidation, which results in C10--C19 bond cleavage, has not been determined. Two proposed mechanisms which remain viable involve either initial 1 beta-hydrogen atom abstraction or addition of the ferric peroxy anion from aromatase to the C19 aldehyde. Semiempirical molecular orbital calculations (AM1) were used to study potential reaction mechanisms initiated by initial 1 beta-hydrogen atom abstraction. Initially, the energetics of carbon--carbon bond cleavage of the keto and enol forms of C1-radicals were studied and were found to be energetically similar. A mechanism was proposed in which the 19-oxo intermediate is subject to initial nucleophilic attack by the protein. The geometry of the A-ring in the androgens is between that for the 1-radicals and estrogen, suggesting that some transition state stabilization for the homolytic cleavage reaction can occur. More recently, studies on liver microsomal cytochrome P450 mediated deformylation of xenobiotic aldehydes supports mechanisms involving an alkyl peroxy intermediate formed by addition of the ferric peroxy anion from aromatase to the C19 aldehyde. Although this intermediate could proceed through several different concerted or non-concerted pathways, one non-concerted pathway involves the heterolytic cleavage of the dioxygen bond resulting in an active oxygenating species (iron-oxene) and a diol. The diol could then undergo hydrogen atom abstraction followed by homolytic carbon--carbon bond cleavage as in the mechanisms modeled previously. When this cleavage was modeled for seven aldehydes, a good correlation with reported experimental aldehyde turnover numbers was obtained. However, when dialkoxy derivatives of the aldehydes are subject to microsomal metabolism, the rates of carbon-carbon cleavage products do not approach the rates of deformylation of the aldehyde analog.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Mar
pubmed:issn
0960-0760
pubmed:author
pubmed:issnType
Print
pubmed:volume
44
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
367-73
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1993
pubmed:articleTitle
Studies on the mechanism of aromatase and other cytochrome P450 mediated deformylation reactions.
pubmed:affiliation
Laboratory of Molecular Carcinogenesis, NCI, National Institutes of Health, Bethesda, MD 20892.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Review