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.