Linked Life Data

2211602

Source:http://linkedlifedata.com/resource/pubmed/id/2211602

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
28
pubmed:dateCreated
1990-11-16
pubmed:abstractText
The reaction pathway of enzyme-catalyzed acetylation of the acyl-accepting sites of the yeast synthase, a Ser-OH at the acetyl transacylase site, a Cys-SH at the beta-ketoacyl synthase site, and the acyl carrier protein 4'-phosphopantetheine-SH (Pant-SH), has been investigated using the chromophoric substrate, p-nitrophenyl thioacetate. The stoichiometry of acetylation of the native enzyme was 3 mol of acetate bound per mol of synthase unit, alpha beta (Mr 430,000). The acetylation process is biexponential; the rate constant of acetylation of the first 2 mol is 5.0 s-1 and the third mol is 0.2 s-1. The pathway by which acetyl moiety is added to the enzyme was determined by selectively blocking the acyl-accepting sites and subsequently determining the kinetics and stoichiometry of acetylation. The dibromopropanone-treated enzyme, in which the Pant-SH and Cys-SH are alkylated, exhibited an exponential burst of approximately 1 mol/mol of synthase unit with a rate constant of 11.0 s-1. The iodoacetamide-treated enzyme, in which Cys-SH is alkylated, had a biexponential burst with a total stoichiometry of approximately 2 mol/mol of synthase unit, with rate constants of 9 and 0.2 s-1, respectively. The kinetically competent acetylation to the extent of 2 and approximately 1 mol/mol of synthase unit for both Cys-SH and Cys-SH and Pant-SH-blocked enzymes, respectively, indicated that the route of acetyl transfer in the yeast synthase is obligatorily Ser-OH----Cys-SH. The acetylation of Pant-SH (0.2 s-1) occurs with a rate insignificant to the process of fatty acid synthesis (turnover rate constant of 1.5 s-1). These conclusions are supported by experiments involving end point radiolabeling of the synthase with [1-14C]acetyl moieties using the substrate, p-nitrophenyl thio[1-14C]acetate. Native, dibromopropanone-treated, and iodoacetamide-treated enzymes bind about 3, 1, and 2 mol of acetyl/mol of synthase unit, respectively. Performic acid oxidation studies of the acetyl-labeled enzyme indicate that there is one Ser-O-acetyl formed in the native and alkylated enzymes and one Cys-S-acetyl and one Pant-S-acetyl formed in the native enzyme. Altogether, these results support our contention that the acetylation of the Pant-SH is kinetically incompetent. Thus, the yeast synthase transacetylation reactions occur by a novel process of acetyl transfer from CoA to Ser-OH----Cys-SH, which is in contrast to the transfer from CoA to Ser-OH----Pant-SH----Cys-SH catalyzed by the prokaryotic synthases.(ABSTRACT TRUNCATED AT 400 WORDS)
pubmed:grant
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
5
pubmed:volume
265
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
16971-7
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1990
pubmed:articleTitle
The yeast fatty acid synthase. Pathway for transfer of the acetyl group from coenzyme A to the Cys-SH of the condensation site.
pubmed:affiliation
Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, U.S. Gov't, Non-P.H.S., Research Support, Non-U.S. Gov't