In vitro secretion of digestive phospholipase A2 by midguts isolated from tobacco hornworms, Manduca sexta
✍ Scribed by Rico L. Rana; David W. Stanley
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 229 KB
- Volume
- 42
- Category
- Article
- ISSN
- 0739-4462
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✦ Synopsis
We report on secretion of phospholipase A 2 (PLA 2 ) by in vitro preparations of midguts isolated from tobacco hornworms, Manduca sexta. This enzyme is responsible for hydrolysis of fatty acids from the sn-2 position of phospholipids, a necessary step in fatty acid absorption. The in vitro midgut preparations are competent to secrete PLA 2 into incubation buffer. Secretion began within the first 30 min of incubation and increased to a maximum at 8 h. We selected 2 h incubations because substantial loss of tissue integrity was observed after 8 h incubations. Using 2 h incubations, we recorded increased secretion of digestive PLA 2 from midguts incubated in buffer amended with diet or with yeast as a component of the diet. We also recorded small increases in secretion of PLA 2 from midguts incubated in buffer amended with a specific phospholipid, phosphatidylcholine. Midguts incubated in buffer amended with increased concentrations of phospholipid did not yield higher levels of PLA 2 activity. Lepidopteran midguts can be divided into three regions, and we recorded the highest secretion of PLA 2 from the middle region and lowest secretion from the anterior region. Because isolated midguts responded to food chemicals with increased secretion of digestive PLA 2 , we suggest that secretion of digestive enzymes in tobacco hornworms is regulated by a prandial and/or paracrine mechanism, as suggested for digestive proteases in other insect species. Arch.