Lipase Activity in the Larval Midgut of Rhynchophorus palmarum: Biochemical Characterization and the Effects of Reducing Agents.

Camilla Camerino Santana,Irinaldo Diniz Basílio Júnior,Ticiano Gomes Do Nascimento,Leandro A Barbosa,Camila Braga Dornelas,Luciano A M Grillo

doi:10.3390/insects8030100

Camilla Camerino Santana, Irinaldo Diniz Basílio Júnior + Show 4 more

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https://doi.org/10.3390/insects8030100

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Abstract

Lipases have key roles in insect lipid acquisition, storage, and mobilization and are also fundamental to many physiological processes in insects. Lipids are an important component of insect diets, where they are hydrolyzed in the midgut lumen, absorbed, and used for the synthesis of complex lipids. The South American palm weevil Rhynchophorus palmarum is one of the most important pests on commercial palm plantations. However, there are few studies about lipid digestion for this insect. In this work, we have described the biochemical characterization of the lipase activity in the posterior midgut of the R. palmarum palm weevil. Lipase activity was highest between the temperatures of 37 °C and 45 °C and at pH 6.5. Lipase activity was also sensitive to variations in salt and calcium concentrations. Lipases have been described structurally as enzymes with the Ser-His-Asp Catalytic Triad, containing an active serine. The serine protease inhibitor PMSF (phenylmethane sulfonyl fluoride) inhibited the lipases from R. palmarum, demonstrating the importance of a serine residue for this activity. The ability of the lipases to hydrolyze p-Nitrophenyl esters with different chain lengths has revealed the activities of a broad range of substrates. The lipase activities of R. palmarum increased in the presence of reduced glutathione (GSH) and dithiothreitol (DTT), while in the presence of oxidized glutathione (GSSG), activities were drastically reduced. To our knowledge, this study has provided the first information about lipase activity in the R. palmarum palm weevil.

Highlights

Lipids are essential for all forms of life and they perform an important array of functions in insects
We investigated the time-course and the effects of protein concentrations of lipase activity of posterior midgut homogenate of R. palmarum larvae
The necessity of this active serine for lipase activity in R. palmarum was assessed through the incubation of phenylmethane sulfonyl fluoride (PMSF) with the homogenates

Summary

Introduction

Lipids are essential for all forms of life and they perform an important array of functions in insects. The main lipids in insects are triacylglycerols (TAGs), diacylglycerols (DAGs), phospholipids, hydrocarbons, and wax esters [1]. Triacylglycerols (TAGs) constitute a major lipid component in the diet of insects and their processes of digestion and absorption are very similar to those in mammals [2]. TAGs are hydrolyzed in the midgut lumen and the products of digestion are absorbed and used for the synthesis of complex lipids [2,3]. TAG-lipases are enzymes that hydrolyze the outer ester links of TAGs. TAG-lipases are enzymes that hydrolyze the outer ester links of TAGs In insects, these enzymes have more affinity to the unsaturated fatty acids, and they are activated by calcium ions [4,5],

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