Tissue and chain length specificity of the fatty acyl-CoA elongation system in the American cockroach

The metabolism and role of free fatty acids in key physiological processes in insects of medical, veterinary and forensic importance

Insects are the most widespread group of organisms and more than one million species have been described. These animals have significant ecological functions, for example they are pollinators of many types of plants. However, they also have direct influence on human life in different manners. They have high medical and veterinary significance, stemming from their role as vectors of disease and infection of wounds and necrotic tissue; they are also plant pests, parasitoids and predators whose activities can influence agriculture. In addition, their use in medical treatments, such as maggot therapy of gangrene and wounds, has grown considerably. They also have many uses in forensic science to determine the minimum post-mortem interval and provide valuable information about the movement of the body, cause of the death, drug use, or poisoning. It has also been proposed that they may be used as model organisms to replace mammal systems in research. The present review describes the role of free fatty acids (FFAs) in key physiological processes in insects. By focusing on insects of medical, veterinary significance, we have limited our description of the physiological processes to those most important from the point of view of insect control; the study examines their effects on insect reproduction and resistance to the adverse effects of abiotic (low temperature) and biotic (pathogens) factors.

Lipid metabolism in Rhodnius prolixus: Lessons from the genome

The kissing bug Rhodnius prolixus is both an important vector of Chagas' disease and an interesting model for investigation into the field of physiology, including lipid metabolism. The publication of this insect genome will bring a huge amount of new molecular biology data to be used in future experiments. Although this work represents a promising scenario, a preliminary analysis of the sequence data is necessary to identify and annotate the genes involved in lipid metabolism. Here, we used bioinformatics tools and gene expression analysis to explore genes from different genes families and pathways, including genes for fat breakdown, as lipases and phospholipases, and enzymes from β-oxidation, fatty acid metabolism, and acyl-CoA and glycerolipid synthesis. The R. prolixus genome encodes 31 putative lipase genes, including 21 neutral lipases and 5 acid lipases. The expression profiles of some of these genes were analyzed. We were able to identify nine phospholipase A2 genes. A variety of gene families that participate in fatty acid synthesis and modification were studied, including fatty acid synthase, elongase, desaturase and reductase. Concerning the synthesis of glycerolipids, we found a second isoform of glycerol-3-phosphate acyltransferase that was ubiquitously expressed throughout the organs. Finally, all genes involved in fatty acid β-oxidation were identified, but not a long-chain acyl-CoA dehydrogenase. These results provide fundamental data to be used in future research on insect lipid metabolism and its possible relevance to Chagas' disease transmission.

Identification of novel C(20) and C (22) trienoic acids from arctiid and geometrid female moths that produce polyenyl Type II Sex pheromone components

Gas chromatography-mass spectrometry (GC-MS) and GC-electroantennographic detection (EAD) analyses of the sex pheromone extract from a wasp moth, Syntomoides imaon (Lepidoptera: Arctiidae: Syntominae), showed that virgin females produced (Z,Z,Z)-3,6,9-henicosatriene and (Z,Z,Z)-1,3,6,9-henicosatetraene with a trace amount of their C(20) analogs. Identification of the chemical structures was facilitated by comparison with authentic standards and the double-bond positions were confirmed by dimethyl disulfide derivatization of monoenes produced by a diimide reduction. In a field test in the Yonaguni-jima Islands, males of the diurnal species were captured in traps baited with a 1:2 mixture of the above-described synthetic C(21) polyenes. Lipids were extracted from the abdominal integument and its associated oenocytes and peripheral fat bodies. Following derivatization, fatty acid methyl esters (FAMEs) were fractionated by HPLC equipped with an ODS column, and methyl (Z,Z,Z)-11,14,17-icosatrienoate and (Z,Z,Z)-13,16,19-docosatrienoate were identified by GC-MS. These novel C(20) and C(22) acid moieties are longer-chain analogs of linolenic acid, (Z,Z,Z)-9,12,15-octadecatrienoic acid. They are presumed to be biosynthetic precursors of the S. imaon pheromone because the C(21) trienyl component might be formed by decarboxylation of the C(22) acid. On the other hand, the C(20) acid, but not the C(22) acid, was found in FAMEs of Ascotis selenaria cretacea (Lepidoptera: Geometridae), which secretes C(19) pheromone components, (Z,Z,Z)-3,6,9-nonadecatriene and the monoepoxy derivative, indicating that different systems of the chain elongation might play an important role in developing species-specific communication systems mediated with polyunsaturated hydrocarbons and/or epoxy derivatives, components of Type II lepidopteran sex pheromones.

Ecological, behavioral, and biochemical aspects of insect hydrocarbons

This review covers selected literature from 1982 to the present on some of the ecological, behavioral, and biochemical aspects of hydrocarbon use by insects and other arthropods. Major ecological and behavioral topics are species- and gender-recognition, nestmate recognition, task-specific cues, dominance and fertility cues, chemical mimicry, and primer pheromones. Major biochemical topics include chain length regulation, mechanism of hydrocarbon formation, timing of hydrocarbon synthesis and transport, and biosynthesis of volatile hydrocarbon pheromones of Lepidoptera and Coleoptera. In addition, a section is devoted to future research needs in this rapidly growing area of science.

Sex pheromone levels in pheromone glands and identification of the pheromone and hydrocarbons in the hemolymph of the moth Scoliopteryx libatrix L. (Lepidoptera: Noctuidae)

The hydrocarbon sex pheromone (13-methyl-Z6-heneicosene) of Scoliopteryx libatrix L. (Lepidoptera: Noctuidae) was found to reach its highest levels on pheromone glands of 3-day-old females. Pheromone levels were not different between the time of maximum calling (end of scotophase) and at the middle of photophase. Overwintering females collected in October had sex pheromone present. Decapitation did not lower the amount of pheromone present, indicating that a head factor is not involved in maintaining pheromone titers. Hemolymph also contained the pheromone, indicating that it is made by oenocytes and transported to the sex pheromone gland. Longer chain length hydrocarbons were also identified from the hemolymph and on the cuticular surface. Quantitative differences in hydrocarbon profiles were found with more methyl-branched hydrocarbons found in the hemolymph than on the cuticular surface. Arch.

Fatty acid elongation in the biosynthesis of (Z)-10-heptadecen-2-one and 2-tridecanone in ejaculatory bulb microsomes of Drosophila buzzatii

A fatty acid chain elongation process is involved in incorporation of saturated and unsaturated fatty acyl-CoA esters into 2-tridecanone and (Z)-10-heptadecen-2-one by Drosophila buzzatii. The microsomal fraction from mature male ejaculatory bulbs is chain-length specific and requires malonyl-CoA (or acetyl-CoA, if acetyl-CoA carboxylase were present) for the chain elongation step to 2-ketones. Decarboxylation of the proposed intermediate beta-ketoacid results in 2-ketone biosynthesis. Incubation of the microsomes with the acetyl-CoA carboxylase inhibitor avidin indicated that acetyl-CoA carboxylase was present in the microsomal preparations; however, washing of the microsomal preparation removed the acetyl-CoA carboxylase activity. Fatty acyl-CoA esters were also chain elongated to produce fatty acids two and four carbons longer, suggesting that the enzymes for normal fatty acid chain elongation are also present in the microsomal fraction from ejaculatory bulbs. How much, if any, of this fatty acid chain elongation system is used for 2-ketone biosynthesis is yet to be determined.

Regulation of sex pheromone biosynthesis in the housefly, Musca domestica: relative contribution of the elongation and reductive steps

The regulation of production of the sex pheromone (Z)-9-tricosene (Z9-23:Hy) in the housefly, Musca domestica, was studied by examining the chain length specificity of the fatty acyl-CoA elongation reactions and the reductive conversion of fatty acyl-CoAs to alkenes in 1- and 4-day-old male and female houseflies. Microsomal preparations from 4-day-old female insects produced as the predominant alkene Z9-23:Hy when incubated with malonyl-CoA, NADPH, and [9,10-3H2]oleoyl-CoA (18:1-CoA), whereas microsomal preparations from 4-day-old male insects produced predominantly (Z)-9-heptacosene (Z9-27:Hy). These are the major alkenes produced in vivo by Day 4 females and males, respectively. Microsomes prepared from both Day 1 males and Day 1 females produced Z9-27:Hy as the major alkene from labeled 18:1-CoA. This is the major alkene produced in vivo by both sexes at Day 1. An examination of the chain length specificity of the elongation reactions showed that microsomes prepared from Day 4 male insects readily elongated both 18:1-CoA and 15-[15,16-3H2]tetracosenoyl-CoA (24:1-CoA) to 28-carbon moieties, whereas microsomes from Day 4 female insects did not efficiently elongate either substrate beyond 24 carbons. With high substrate concentrations, microsomes prepared from male insects converted 24:1-CoA to Z9-23:Hy more efficiently than did those from females, whereas under lower and presumably more physiological substrate concentrations, microsomes from females had slightly higher activity than did those from males. Taken together, these data show that the regulation of the chain length of the alkenes, and thus sex pheromone production, in the housefly resides predominantly in the elongation reactions and not in the step which converts the fatty acyl-CoA to hydrocarbon.

A microsomal fatty acid synthetase from the integument of Blattella germanica synthesizes methyl-branched fatty acids, precursors to hydrocarbon and contact sex pheromone

Methyl-branched fatty acids present in the integument of the German cockroach, Blattella germanica, were identified by gas chromatography-mass spectrometry of their methyl esters and reduction products (alkanes) as n-3-, n-4-, n-5-, n-7-, n-8-, and n-9-monomethyl fatty acids and as n-5,9-, n-3,9-, and n-3,11-dimethyl fatty acids with 16 to 20 total carbons. These fatty acids have the same branching patterns as do the major hydrocarbons of this insect, including 3,11-dimethylnonacosane, the precursor to the major contact sex pheromone, and are presumed to be intermediates in hydrocarbon formation. A novel microsomal fatty acid synthetase (FAS) located in the integument of this insect incorporated [methyl-14C]methylmalonyl-CoA into methyl-branched fatty acids as demonstrated by radio-high-performance liquid chromatography. A cytosolic FAS is also present in the integument. Both the microsomal and the soluble FAS incorporated [methyl-14C]methylmalonyl-CoA into fatty acids, but only the microsomal FAS was able to efficiently use methylmalonyl-CoA as the sole elongating agent. This is the first report of the characterization of methyl-branched fatty acids from the integument of an insect and of an integumental microsomal FAS that incorporates methylmalonyl-CoA into branched fatty acids.

Alkane biosynthesis by decarbonylation of aldehyde catalyzed by a microsomal preparation from Botryococcus braunii

The final step in the synthesis of n-hydrocarbons in an animal and a higher plant involves enzymatic decarbonylation of aldehydes to the corresponding alkanes by loss of the carbonyl carbon. Whether such a novel reaction is involved in hydrocarbon synthesis in the colonial microalga, Botryococcus braunii, which is known to produce unusually high levels (up to 32% of dry weight) of n-C27, C29, and C31 alka-dienes and -trienes, was investigated. Dithioerythritol severely inhibited the incorporation of [1-14C]acetate into these hydrocarbons with accumulation of the label in the aldehyde fraction in the B. braunii cells. Microsomal preparations of the alga synthesized alkane from fatty acid and aldehyde in the absence of O2. Conversion of fatty acid to alkane required CoA, ATP, and NADH, whereas conversion of aldehyde to alkane did not require the addition of cofactors. That the alkane synthesis involves a decarbonylation was shown by the production of CO and heptadecane from octadecanal. CO was identified by adsorption to RhCl[(C6H6)3P]3. The decarbonylase had a pH optimum at 7.0, an apparent Km of 65 microM, a Vmax of 1.36 nmol/min/mg and was inhibited by the metal chelators EDTA, O-phenanthroline and 8-hydroxyquinoline. It was stimulated nearly threefold by 2 mM ascorbate and inhibited by the presence of O2. A partial (28%) retention of the aldehydic hydrogen of [1-3H]octadecanal in the heptadecane was observed; the remaining 3H was lost to H2O. The microsomal preparation also catalyzed the oxidation of 14CO to 14CO2, with a pH optimum of 7.0. This accounts for the nonstoichiometry of CO to heptadecane observed. In vivo studies with 14CO showed that the label was incorporated into metabolic products. This metabolic conversion of CO, not found in the previously examined hydrocarbon synthesizing systems, may be necessary for organisms that produce large amounts of hydrocarbons such as the present alga. The mechanism of the decarbonylation and the nature of the decarbonylase remain to be elucidated.

Characterization of the delta 12 desaturase in the American cockroach, Periplaneta americana: the nature of the substrate

The cockroach, Periplaneta americana, can convert oleic acid (18:1(n - 9], to linoleic acid, (18:2(n - 6], by a microsomal delta 12 desaturase. Most of the desaturase activity was present in the fat body tissue, with lower activity in the epidermis and no detectable activity in the thorax or gut tissue. In incubations of microsomal preparations from fat body tissues with [1-14C]18:1-CoA, increased amounts of [1-14C]18:2 were found with increasing time and protein concentration. The form of the substrate for the delta 12 desaturase was determined to be 18:1-CoA by comparing activity towards [1-14C]18:1-CoA and [1-14C]18:1 transesterified to phospholipid. Ozonolysis of the 18:2 formed from [1-14C]oleoyl-CoA followed by radio-gas-liquid chromatography gave one labeled peak, 9-oxononanoate, which showed that the product of the delta 12 desaturase is the physiologically important isomer, 18:2(n - 6).