Studies on the cholesterol ester hydrolase of Trogoderma (Coleoptera)

Area of Science:

• Biochemistry
• Entomology
• Insect Physiology

Background:

• The khapra beetle (Trogoderma granarium) is a significant pest of stored grains.
• Understanding insect enzymes is crucial for developing targeted pest control strategies.

Purpose of the Study:

• To characterize the enzyme cholesterol ester hydrolase (EC 3.1.1.13) in Trogoderma granarium larvae.
• To investigate the enzyme's properties, including optimal conditions, substrate specificity, and inhibitors.

Main Methods:

• Enzyme assays were performed on extracts from khapra beetle larvae.
• pH and temperature optima were determined.
• Molecular weight was estimated.
• Substrate hydrolysis and inhibition patterns were analyzed.
• Subcellular fractionation was used to localize enzyme activity.

Main Results:

• Cholesterol ester hydrolase was detected in Trogoderma granarium larvae.
• The enzyme exhibited optimal activity at pH 6.6 and 37°C.
• Its molecular weight was estimated to be 76,000-80,000 Da.
• The enzyme effectively hydrolyzed cholesteryl acetate, stearate, and oleate.
• Cholesterol chloride and methyl ether inhibited the enzyme, as did p-hydroxymercuribenzoate, with inhibition reversed by dithiothreitol, reduced glutathione, or cysteine.
• Enzyme activity was primarily found in the 104,000 g fraction.

Conclusions:

• Trogoderma granarium larvae possess a cholesterol ester hydrolase with specific biochemical properties.
• The enzyme's substrate specificity and inhibition profile provide insights into its function.
• Understanding this enzyme may aid in developing novel control methods for this agricultural pest.