Midgut metabolism in different instars of the tobacco hornworm (Manduca sexta)

✍ Scribed by Gibellato, C. M. ;Chamberlin, M. E.

• Publisher: John Wiley and Sons
• Year: 1994
• Tongue: English
• Weight: 521 KB
• Volume: 270
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402700410

✦ Synopsis

Abstract

Enzyme activities and mitochondrial substrate oxidation were measured in the posterior midguts of tobacco hornworms at different larval stages. A comparison of third, fourth, and fifth instars demonstrated no differences in citrate synthase activity (per gram of midgut), indicating that maximal aerobic capacity is unchanged during larval growth. The midguts of fifth instars had the highest activity of 3‐hydroxyacyl‐CoA dehydrogenase and carnitine acetyltransferase. Furthermore, mitochondria isolated from the midguts of fifth instar larvae had higher rates of palmitoyl carnitine oxidation when compared to mitochondria isolated from the fourth instar larvae. These results indicate that there is an increased preference for fatty acid oxidation in the midguts of fifth instar larvae. The presence of succinyl‐CoA ketotransferase and acetoacetyl‐CoA thiolase as well as the mitochondrial oxidation of acetoacetate and β‐hydroxybutyrate indicate that ketone bodies can serve as substrates for the midgut. The activities of malic enzyme and glucose‐6‐phosphate dehydrogenase were significantly higher in fifth instars than in fourth instars, indicating an increased capacity for lipid synthesis. © Wiley‐Liss, Inc.