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

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.

Purification and characterization of fat body lipase from the Greater Wax MothGalleria mellonella(Lepidoptera: Pyralidae)

“…Similar results were shown for other insects; [38] and Santana et al [41] showed that the activity of lipase from R . prolixus and Rhynchophorus palmarum increased by increasing calcium ion concentrations respectively.…”

“…High temperature may interfere with hydrogen bond of enzyme causing denaturation of this enzyme [32]. Similar results have been shown in other insect lipases, as in gypsy moth Lymantria dispar [40], Rhynchophorus palmarum [41] and N . aenescens [16].…”

“…There are several ways by which ions can affect enzyme activity; one of these ways is keeping the enzyme and substrate near to each other to enhance enzyme activity. Also they preclude the unwanted reaction of nucleophiles and put the active groups of enzyme and substrate in the most perfect position leading to increase the ability of enzyme-substrate complex and enzyme stability [41].…”

“…The previous results indicated that fat body lipase requires metal ions specially calcium, and have a serine residue at their active site. The effect of PMSF was also shown in TAG-lipase activity from the reproductive accessory glands of the sand fly Phlebotomus papatasi [46] and Rhynchophorus palmarum [41]. Also it was proven that the active-site serine residue is part of a preserved sequence (GXSXG) that has been found in most lipase sequences of mammals and prokaryotes [47, 48, 49] and invertebrate lipases such as insects [2, 38] and crustaceae [50].…”

Purification and characterization of fat body lipase from the greater wax moth, Galleria mellonella (Lepidoptera: Pyralidae)

“…High temperature may interfere with the hydrogen bond of enzyme causing denaturation of this enzyme (Zeng and Cohen, 2000a). Parallel results have been revealed in other insect lipases, as in gypsy moth Lymantria dispar (Mrdaković et al 2008), Rhynchophorus palmarum (Santana et al 2017) and N. aenescens (Zibaee, 2012). In contrast, some invertebrates showed the highest activity of lipase at 60°C such as the Mediterranean green crab Carcinus mediterraneus (Cherif et al, 2007) and the Antarctic krill Euphasia superba (Barriga González, 2006).…”