Carbon isotopic fractionation in the biosynthesis of bacterial fatty acids. Ozonolysis of unsaturated fatty acids as a means of determining the intramolecular distribution of carbon isotopes

Details Carbon isotopic fractionation in the biosynthesis of bacterial fatty acids. Ozonolysis of unsaturated fatty acids as a means of determining the intramolecular distribution of carbon isotopes Carbon isotopic fractionation in the biosynthesis of bacterial fatty acids. Ozonolysis of unsaturated fatty acids as a means of determining the intramolecular distribution of carbon isotopes

Feb 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982gecoa..46..139m&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 46, Issue 2, pp.139-149

Mathematics

Logic

8

Scientific paper

Methods for the determination of 13 C abundances at individual olefinic carbon positions have been developed, tested, and shown to perform accurately. 1. (1) The double bond is oxidized with ozone; 2. (2) silver oxide is used to cleave the resulting ozonide quantitatively to carboxylic-acid fragments; 3. (3) a modified Schmidt decarboxylation is used to produce CO 2 quantitatively from the carboxyl groups of the separated cleavage products; 4. (4) the CO 2 is utilized for mass spectrometric analysis. The results of intramolecular isotopic analyses are combined with molecular-average isotopic compositions determined by total combustion in order to show that fatty acids biosynthesized by Escherichia coli grown aerobically with glucose as the sole carbon source and harvested at late log phase are depleted by approximately 3%. in 13 C relative to the glucose. This fractionation arises in the formation of acetylcoenzyme A by pyruvate dehydrogenase and is localized at the carboxyl position in the acetyl-CoA product. The isotopic order in that two-carbon subunit is carried through the biosynthesis of fatty acids so that alternate positions in the fatty-acid chains are depleted in 13 C by an amount equal to twice the molecular-average depletion. The kinetic isotope effect at C-2 for pyruvate dehydrogenase in vivo is shown to be approximately 2.3%. While it appears that no other fractionation mechanism has controlled the overall depletion of 13 C in these fatty acids, a separate process responsible for control of isotopic abundances in the carboxyl groups has been identified and described elsewhere [Monson K.D. and Hayes J.M. (1980) J. Biol. Chem. 255 , 11435-11441]. It is concluded that kinetic, rather than thermodynamic, factors have controlled isotopic distributions in these cells and that kinetic factors will be dominant in most biological reactions.

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