Studies on the Mechanism of Fatty Acid Synthesis
XIII. THE ROLE OF 
-HYDROXY ACIDS IN THE SYNTHESIS OF PALMITATE AND CIS-VACCENATE BY THE ESCHERICHIA COLI ENZYME SYSTEM
E. L. Pugh 1, F. Sauer 1, Moseley Waite 1, Richard E. Toomey 1, and Salih J. Wakil 1
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1 From the Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27706
The fatty acid-synthesizing system of Escherichia coli was fractionated by chromatography on diethylaminoethyl cellulose into three different enzyme fractions: Eii, Eiii, and Eiv. Incubation of Fraction Eii with acetyl coenzyme A, malonyl coenzyme A, reduced triphosphopyridine nucleotide, and acyl carrier protein (ACP) yielded ß-hydroxydecanoyl-ACP, ß-hydroxylauryl-ACP, and ß-hydroxymyristyl-ACP in variable amounts depending on the Eii preparations. Addition of Fraction Eiii to reaction mixtures of Fraction Eii yielded mainly palmitic acid, whereas the addition of Fraction Eiv to the same Eii reaction mixture yielded mainly cis-vaccenic acid. Therefore, Fractions Eiii and Eiv must have directed the synthesis of saturated and unsaturated fatty acids from ß-hydroxydecanoyl-ACP, respectively.
Isolated ß-hydroxyacyl-ACPs could be converted to their saturated homologues by incubation with Fraction Eiii and TPNH or could be elongated to palmitic acid by incubation with Fraction Eiii, TPNH, malonyl-CoA, and Fraction Eii.
Incubation of Fraction Eiii or its subfractions with ß-hydroxydecanoyl-CoA yielded the 2-decenoyl derivative. Incubation of Fraction Eiv or its subfractions with ß-hydroxydecanoyl-CoA yielded a mixture of cis-3-decenoyl and trans-2-decenoyl derivatives. The relationship between the two dehydrases and the various products formed are discussed as well as their role in the synthesis of saturated and unsaturated fatty acids.
Submitted on July 2, 1965
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