Biosynthesis of Linoleic Acid in Insects

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Vertebrates cannot synthesize and thus require a dietary source of linoleic acid, 18:2(n-6), which is used both as a structural component of membranes and as precursor for physiologically important eicosanoids. Until recently, it had been thought that insects, as is the case for vertebrates, were unable to synthesize linoleic acid. Studies have demonstrated that some, but not all, insect species possess a delta-12 desaturase and are thus able to produce linoleic acid. This proposal is designed to examine this synthesis of linoleic acid in the cockroach, Periplaneta americana, the aphid, Acyrthosiphon pisum, and the cricket, Acheta domesticus. Emphasis will be on studies designed to unambiguously rule out the contribution of microorganisms, both symbiotic and exterior, to linoleate synthesis, ie. that it is the insect tissue that is responsible for the desaturation of oleate to linoleate. In addition, the form of the substrate for the delta-12 desaturase and the further elongation and desaturation of linoleic acid will be examined. These studies will characterize the unique process by which certain insect species have gained a nutritional independence from dietary requirements for polyunsaturated fatty acids. Significant fundamental knowledge of comparative lipid metabolism will be obtained from this work. Linoleic acid is an essential fatty acid for vertebrates. It is an important membrane component and serves as a precursor for hormone-like substances that regulate many cell functions. Vertebrates lack the ability to synthesize linoleic acid and fulfill their dietary requirement by the consumption of plants, which, in addition to protozoa and fungi readily synthesize the fatty acid. Until recently, it was thought that insects, like other animals, were unable to synthesize linoleic acid. Recent evidence now suggests that insects do have this capability. This research will examine this phenomenon. It will provide a basic understanding of linoleic acid biosynthesis in insects and may have future implications for the exploitation of the insect-specific pathways of hormone regulation as a means of pest control.