Biochemistry of the development of the insect Ceratitis capitata. In vitro biosynthesis of fatty acids from 14C-acetate during metamorphosis

Acetyl CoA generation and N-acetylation of serotonin (5HT) in the mosquito, Aedes togoi

Acetyl CoA synthetase (ACS; EC 6.2.1.1) was studied in the mosquito, Aedes togoi, by a novel assay which coupled the acetyl-CoA generated to p-aminosalicylic acid (ASA). The N-acetylated product was determined by an HPLC-fluorimetric procedure. High ACS activity was observed in the newly-pupated pupae of both sexes and in the adult male mosquito whose activity was five times that of the female. Acetyl CoA-dependent N-acetyltransferase (NAT; EC 2.3.1.5) activity toward serotonin (5HT) was also studied using HPLC-electrochemical detection (HPLC-ECD). A progressive increase in the 5HT-NAT activity was observed from the fourth-instar larvae to the adult mosquito with the latter showing 6-fold higher activity in the head compared to the abdomen-thorax region. Kinetic studies on the pupal enzyme extracts showed that the apparent Km values for 5HT and acetyl CoA were 63 and 66 microM respectively. Tryptamine inhibited 5HT-NAT non-competitively with a Ki value of 8 microM.

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.

Neutral lipid composition of Culex quinquefasciatus and Culex tritaeniorhynchus cells at two phases of growth

The mosquito cells Culex quinquefasciatus and Culex tritaeniorhynchus were grown in spinner cultures. The fatty acid profiles of the neutral lipid classes were analyzed, and comparisons were made between the two species at logarithmic and stationary phases of growth and between the species and the medium. The results from the data suggest an increase in the average chain length of the fatty acids in the free fatty acid and sterol ester fractions of the Culex quinquefasciatus cells with aging. From the logarighmic to stationary phase, both Culex cells showed some increase in desaturation of acids in the di- and triglyceride and free fatty acid fractions. The Culex tritaeniorhynchus cells also showed some increase in desaturation of acids in the monoglyceride fraction. Differences between the two Culex species at the logarithmic phase of growth were observed in the fatty acid profiles of all the neutral lipid fractions examined and at the stationary phase of growth in the free fatty acid, triglyceride, and sterol ester fractions.

Methylating activity of (methyl-14C)-S-adenosylmethionine by microsomes of the insect Ceratitis capitata

The methylating activity of (methyl-14C)-S-adenosylmethionine by microsomes from different stages of development of the insect Ceratitis capitata was studied in a series of in vitro experiments. Larval and pharate adult microsomal preparations were used in the in vitro conditions, and the utilization of the methyl group of the S-adenosylmethionine for the synthesis of phospholipids was evaluated. Incorporation of radioactivity in lipids by pharate adult microsomes was significantly higher than that by larval preparations. In both cases, phosphatidyl ethanolamine showed the highest levels of radioactivity incorporation. Free bases from total lipid hydrolysates were resolved by paper chromatography, and the labeling was investigated by radioactivity scanning of paper chromatograms. Larval and pharate adult preparations showed clearly the presence of dimethylethanolamine and choline. The presence in the incubation media of phosphatidyldimethylethanolamine and deoxycholate enhanced the radioactivity incorporation into choline, whereas, the first stages of methylation were inhibited. These findings confirmed previous results using insect homogenates.

On methylating activity of L-(methyl-14C)-methionine in metabolism of phospholipids by insect Ceratitis capitata

The methylating activity of L-(methyl-14C)-methionine in different stages of developmenent of the insect Ceratitis capitata was studied in a series of in vitro and in vivo experiments. Larval and pharate adult homogenates of the insect were used in the in vitro conditions, and the utilization of the methyl group of methionine for the synthesis of different classes of phospholipids was evaluated. Incorporation of radioactivity in lipids by pharate adult homogenates was significantly higher than that by larval homogenates. In both cases, phosphatidyl ethanolamine showed the highest levels of radioactivity incorporation. Free bases from total lipid hydrolysates were resolved and identified by paper chromatography, and the labeling was investigated by radioactivity scanning of paper chromatograms. Significant differences were observed in the activity of both stages of development of the insect. Larval and pharate adult homogenates incorporated mainly the labeled methyl groups into ethanolamine. Monmethyl ethanolamine was the only methyl derivative that appeared in the hydrolysates of lipids synthesized by larval homogenates, whereas mono-,di-and trimethyl ethanolamine clearly were detected in those synthesized by pharate adult homogeneates. Administration of L-(methyl 14C)-methionine to larvae confirmed the existence of methylation reactions in the metabolic activity of the insect.