Lipoprotein lipase (LpL) activity in Manduca sexta flight muscle tissue was measured using in vivo radiolabeled lipophorin as a substrate. LpL hydrolyses diacylglycerol in the low density lipophorin (that occurs during flight) at a higher rate than diacylglycerol in the high density lipophorin (present in the resting insect). LpL has a pH-optimum of 7.5 and is less sensitive to NaCl than mammalian LpL. LpL is inhibited by bovine albumin and chicken ovalbumin. LpL is inhibited by the serine protease inhibitors diisopropylfluorophosphate (DFP) and phenylmethanesulfonyl fluoride (PMSF), which indicates the presence of an active site serine similar to mammalian LpL. Flight muscle LpL shows affinity for immobilized copper as well as for immobilized heparin. Using radiolabeled DFP, a protein of 37 kDa was identified (after SDS-PAGE) as the DFP-binding protein in a partially purified preparation of LpL. This 37 kDa protein is proposed to be the LpL or a subunit thereof.