Changes of the positional distribution of fatty acids in phosphoglycerides during development of insects

Analysis of lipids in the salivary glands of Amblyomma americanum (L.): detection of a high level of arachidonic acid

Analysis of lipids in salivary glands of the lone star tick, Amblyomma americanum, demonstrated that arachidonic acid (20:4, n-6) comprises 8% of all fatty acids identified by gas chromatography. The occurrence of arachidonic acid and other C20 polyunsaturated fatty acids in tick salivary glands was confirmed by gas chromatography-mass spectrometry. Arachidonate is located entirely in the phospholipid fraction and is associated exclusively with phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Salivary glands stored and frozen for several months had a similar lipid composition as freshly dissected salivary glands, with the exception of a small amount of free arachidonic acid and an increase in lysophosphatidylcholine. Incubation of salivary gland homogenates with snake venom phospholipase A2 showed that most saturated fatty acids are esterified in the sn-1 position of PC and PE, with the unsaturated fatty acids in the sn-2 position. Approximately 75% of arachidonic acid is in the sn-2 position of PC and PE, adding support to the hypothesis that arachidonic acid is released into the cytoplasm after activation of a phospholipase A2 for subsequent metabolism to prostaglandins and/or other eicosanoids.

Biochemistry of development in insects. Triacyglycerol and phosphoglyceride biosynthesis by subcellular fractions

1. A different biochemical behaviour has been previously shown during several stages of the development of the insect Ceratitis capitata; thus, the acyl transferase activity has a different participation in the pathways of synthesis of triacylglycerols and phosphoglycerides by either larval or pharate adult stages of development. The results reported here are concerned with the behavior of mitochondria and microsomes from larvae and pharate adults for the synthesis of triacylglycerols and phosphoglycerides. In all preparations of either mitochondrial or microsomal fractions the optimum protein amount, previously determined, has been used. 2. The highest incorporation of [14C]palmitate into triacylglycerols and phosphoglycerides was achieved by the microsomal fraction from the larval stage of development of the insect. However, mitochondrial fractions from pharate adults utilized higher levels of [14C]palmitate than the microsomal preparation. These differences were not correlated with the palmitoyl-CoA synthetase activity. 3. Glycerol 3-phosphate influenced the fatty acid incorporation in a different manner depending on the stage of development of the insect. Increasing concentrations of glycerol 3-phosphate stimulated the synthesis of triacylglycerols by microsomal and mitochondrial preparations. This effect was not exhibited by the subcellular preparations of pharate adults. 4. Double-label experiments using [14C]glycerol 3-phosphate and[3H]palmitate showed qualitative differences in the synthesis of triacylglycerols by mitochondrial preparations from either larvae of pharate adults. Incorporation of the labelled fatty acids to endogenous triglycerides was preferentially shown by the mitochondria larval preparations. The pathways of synthesis of triacylglycerols and phosphoglycerides by microsomal preparations showed only quantitative differences depending on the stage of development of the insect. 5. Acylation of 14C-labelled lyso-phosphatidylcholine and 14C-labelled lyso-phosphatidylethanolamine by [3H]olate was assayed in the presence of miochondrial and microsomal preparations from the different stages of development of the insect. Microsomal fractions showed an efficient acyl transferase activity mainly when lyso-phosphatidyl-ethanolamine was used as a substrate.

Phospholipid composition of Culex quinquefasciatus and Culex tritaeniorhynchus cells in logarithmic and stationary growth phases

Culex quinquefasciatus and Culex tritaeniorhynchus cells were grown in spinner culture and harvested in logarithmic and stationary phases of growth. The phospholipids were extracted from the cells, and the fatty acid profiles of the phospholipid classes were determined and compared. The major components were phosphatidylcholine and phosphatidylethanolamine, constituting greater than or equal to 80% of the phospholipid. The fatty acid profiles of lysophosphatidylcholine, phosphatidylinositol, and cardiolipin showed changes with aging of the Culex cells and between the species. In the lysophosphatidylcholine fraction, there was an increase in saturation of the fatty acids of the C. quinquefasciatus cells, and chain lengthening occurred in both species from the logarithmic to stationary phases of growth. In the phosphatidylinositiol fraction, both Culex species showed a decrease in monoenes and an increase in polyenes, while only the C. tritaeniorhynchus cells showed an increase in fatty acid chain length with aging. The C. quinquefasciatus cells had an increase in polyenes with aging in the cardiolipin fraction. Differences in the percentage composition of the fatty acids were shown in all the phospholipid fractions between the Culex species in the logarithmic phase of growth and all except the phosphatidylinositiol and cardiolipin fractions in the stationary phase.

Biochemistry of development in insects. Incorporation of fatty acids into different lipid classes

1. To study the different metabolic behaviour of various stages of development of the insect Ceratitis capitata, the incorporation of labelled decanoic, lauric, myristic, palmitic, stearic, oleic, and linoleic acids into triacylglycerols by insect homogenates was investigated. The time-course of incorporation of labelled fatty acids was firstly studied by using oleic acid; it showed that after 10 min of incubation the levels of radioactivity incorporated into triacylglycerols and those remaining in the free fatty acids were practically unchanged. 2. All labelled fatty acids were efficiently incorporated by larval homogenates; however, most of the radioactivity remained as free fatty acids in the presence of pharate adult homogenates, palmitic, and stearic acids being the most scarcely incorporated by this stage of development of the insect. 3. Plots of triacylglycerol and free fatty acid radioactivites versus the stage of development defined a crossing-zone in coincidence with the larval-pupal apolysis. This metabolic difference between larval and pharate adult homogenates could not be explained through differences in the acyl-CoA synthetase activity of the insect; this enzyme activity was notably higher in pharate adult homogenates than in the larval homogenates whatever would be the nature of the fatty acid. 4. [14C]Triolein was scarcely hydrolyzed by both larval and pharate adult homogenates. 5. Double-label experiments were carried out by incorporating either [3H]oleic acid or [3H]-palmitic acid and [14C]glycerol 3-phosphate by larval and pharate adult homogenates at different incubation intervals. Diacylglycerols, triacylglycerols, and phosphoglycerides were isolated and the 14C/3H molar ratio calculated. Results suggest the existence of a different acyltransferase activity in the different stages of development of the insect.