Analysis of the Initial Reactions of Plant Fatty Acid Synthesis

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Fatty acid biosynthesis in plants is a primary metabolic pathway that is necessary to provide the fatty acyl components found in the lipids of membranes and vegetable oils. The initial sequence of reaction for this pathway are under reevaluation since a new condensing enzyme, 3-ketoacyl-ACP synthase II (KAS III), was discovered in spinach. KAS III has properties in vitro that are consistent with it being the enzyme that catalyzes the initial priming reaction of fatty acid synthesis. The objective of this proposal is to obtain in vivo evidence that it is an essential component of fatty acid synthesis and normally acts to catalyze the initial condensation. In addition, the metabolic role of acetyl- CoA-ACP transacylase and KAS I will be reevaluated. Previously, these two enzymes were thought to initiate fatty acid synthesis. The biochemical characterization of KAS III to be completed includes substrate specificity and level of acetyl-CoA-ACP transacylase activity copurifying with KAS III. The effects on rates of, and regulation of fatty acid synthesis will be evaluated. IN addition, the in vivo role of KAS III and acetyl-CoA-ACP transacylase will be evaluated using isolated chloroplasts. The results of this proposal should help to determine the initial steps of fatty acid biosynthesis in plants.//