Linked Life Data

1736884

Source:http://linkedlifedata.com/resource/pubmed/id/1736884

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:dateCreated
1992-3-11
pubmed:abstractText
Mushroom tyrosinase, which is known to convert a variety of o-diphenols into o-benzoquinones, has been shown to catalyse an unusual oxidative decarboxylation of 3,4-dihydroxymandelic acid to 3,4-dihydroxybenzaldehyde [Sugumaran (1986) Biochemistry 25, 4489-4492]. The mechanism of this reaction was re-investigated. Although visible-region spectral studies of the reaction mixture containing 3,4-dihydroxymandelic acid and tyrosinase failed to generate the spectrum of a quinone product during the steady state of the reaction, both trapping experiments and non-steady-state kinetic experiments provided evidence for the transient formation of unstable 3,4-mandeloquinone in the reaction mixture. The visible-region spectrum of mandeloquinone resembled related quinones and exhibited an absorbance maximum at 394 nm. Since attempts to trap the second intermediate, namely alpha,2-dihydroxy-p-quinone methide, were in vain, mechanistic studies were undertaken to provide evidence for its participation. The decarboxylative quinone methide formation from 3,4-mandeloquinone dictates the retention of a proton on the alpha-carbon atom. Hence, if we replace this proton with deuterium, the resultant 3,4-dihydroxybenzaldehyde should retain the deuterium present in the original substrate. To test this hypothesis, we chemoenzymically synthesized alpha-deuterated 3,4-dihydroxymandelic acid and examined its enzymic oxidation. Our studies reveal that the resultant 3,4-dihydroxybenzaldehyde retained nearly 90% of the deuterium, strongly indicating the transient formation of quinone methide. On the basis of these findings it is concluded that the enzymic oxidation of 3,4-dihydroxymandelic acid generates the conventional quinone product, which, owing to its unstability, is rapidly decarboxylated to generate transient alpha,2-dihydroxy-p-quinone methide. The coupled dienone-phenol re-arrangement and keto-enol tautomerism of this quinone methide produce the observed 3,4-dihydroxybenzaldehyde.
pubmed:grant
pubmed:commentsCorrections
http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-14031389, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-1799672, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-1908223, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-2007565, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-2134172, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-2211605, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-2500362, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-2846069, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-3094574, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-3112146, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-3146978, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-3169236, http://linkedlifedata.com/resource/pubmed/commentcorrection/1736884-6308414
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jan
pubmed:issn
0264-6021
pubmed:author
pubmed:issnType
Print
pubmed:day
15
pubmed:volume
281 ( Pt 2)
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
353-7
pubmed:dateRevised
2009-11-18
pubmed:meshHeading
pubmed:year
1992
pubmed:articleTitle
Mechanistic studies on tyrosinase-catalysed oxidative decarboxylation of 3,4-dihydroxymandelic acid.
pubmed:affiliation
Department of Biology, University of Massachusetts, Boston 02125.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S.