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Plant Physiol, January 2000, Vol. 122, pp. 275-282
Biosynthesis and Elongation of Short- and
Medium-Chain-Length Fatty Acids
Rutger S.
van der Hoeven and
John C.
Steffens*1
Department of Plant Breeding and Biometry, 252 Emerson Hall,
Cornell University, Ithaca, New York 14853.
Short- and medium-chain-length fatty
acids (FAs) are important constituents of a wide array of natural
products. Branched and straight short-chain-length FAs originate from
branched chain amino acid metabolism, and serve as primers for
elongation in FA synthase-like reactions. However, a recent model
proposes that the one-carbon extension reactions that utilize
2-oxo-3-methylbutyric acid in leucine biosynthesis also catalyze a
repetitive one-carbon elongation of short-chain primers to
medium-chain-length FAs. The existence of such a mechanism would
require a novel form of regulation to control carbon flux between amino
acid and FA biosynthesis. A critical re-analysis of the data used to
support this pathway fails to support the hypothesis for FA elongation
by one-carbon extension cycles of -ketoacids. Therefore, we tested
the hypothesis experimentally using criteria that distinguish between
one- and two-carbon elongation mechanisms: (a) isotopomer patterns in
terminal carbon atom pairs of branched and straight FAs resulting from differential labeling with [13C]acetate; (b)
[13C]threonine labeling patterns in odd- and even chain
length FAs; and (c) differential sensitivity of elongation reactions to
inhibition by cerulenin. All three criteria indicated that biosynthesis
of medium-chain length FAs is mediated primarily by FA synthase-like reactions.
1
Present address: Novartis Agribusiness
Biotechnology Research, 3054 Cornwallis Road, Research Triangle Park,
NC 27709-2257.
*
Corresponding author; e-mail
john.steffens{at}nabri.novartis.com; fax 919-541-8557.
© 2000 American Society of Plant Physiologists
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