Submitted on April 6, 2006
Revised on September 7, 2006
Accepted on September 27, 2006
The main triglyceride-lipase from the insect fat body is an active phospholipase A1: Identification and functional characterization of the phospholipase activity
Estela L. Arrese, Rajesh T. Patel, and Jose L. Soulages
Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078
Corresponding Author: estela{at}biochem.okstate.edu
The main triglyceride-lipase (TG-lipase) from the fat body of Manduca sexta has been identified as the homolog of Drosophila melanogaster CG8552. This protein is conserved among insects and also shares significant sequence similarity with vertebrate phospholipases from the PA-PAL1 family. It is shown here that the TG-lipase is also a phospholipase. TG-lipase and phospholipase activities co-purify and are inhibited, or resistant, to the same lipase inhibitors indicating that both activities are catalyzed by the same enzyme and active site. The phospholipase activity of TG-lipase corresponded to phospholipase type A1. The concentration-dependence of lipase activity with TG and PL micellar substrates showed saturation kinetics with apparent Kms of 152 ± 11 µM and 7.8 ± 1.1 µM, respectively. TG-lipase was able to hydrolyze the major phospholipid components of the lipid droplets, PC and PE. The enzyme hydrolyzes 77 molecules of TG for every molecule of PL contained in the lipid droplets. It was observed that the activation of lipolysis in vivo is accompanied by activation of the hydrolysis of phospholipids of the lipid droplets. These results suggest that phospholipase activity of the insect TG-lipase could be required to allow access of the lipase to TG molecules contained in the core of the lipid droplets.
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