PLANT PHYSIOLOGY , Vol 107, Issue 2 413-419, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
The Utilization of Glycolytic Intermediates as Precursors for Fatty Acid Biosynthesis by Pea Root Plastids
Q. Qi, K. F. Kleppinger-Sparace and S. A. Sparace
Plant Sciene Department, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Sainte Anne de Bellevue, Quebec, Canada H9X 3V9
Radiolabeled pyruvate, glucose, glucose-6-phosphate, acetate, and malate
are all variously utilized for fatty acid and glycerolipid biosynthesis by
isolated pea (Pisum sativum L.) root plastids. At the highest
concentrations tested (3-5mM), the rates of incorporation of these
precursors into fatty acids were 183, 154, 125, 99 and 57 nmol h-1 mg-1
protein, respectively. In all cases, cold pyruvate consistently caused the
greatest reduction, whereas cold acetate consistently caused the least
reduction, in the amounts of each of the other radioactive precursors
utilized for fatty acid biosynthesis. Acetate incorporation into fatty
acids was approximately 55% dependent on exogenously supplied reduced
nucleotides (NADH and NADPH), whereas the utilization of the remaining
precursors was only approximately 10 and 20% dependent on added NAD(P)H. In
contrast, the utilization of all precursors was greatly dependent (85-95%)
on exogenously supplied ATP. Palmitate, stearate, and oleate were the only
fatty acids synthesized from radioactive precursors. Higher concentrations
of each precursor caused increased proportions of oleate and decreased
proportions of palmitate synthesized. Radioactive fatty acids from all
precursors were incorporated into glycerolipids. The data presented
indicate that the entire pathway from glucose, including glycolysis, to
fatty acids and glycerolipids is operating in pea root plastids. This
pathway can supply both carbon and reduced nucleotides required for fatty
acid biosynthesis but only a small portion of the ATP required