MANDUCA-SEXTA LIPID TRANSFER PARTICLE - SYNTHESIS BY FAT-BODY AND OCCURRENCE IN HEMOLYMPH

Lipid transfer particle (LTP) is present in hemolymph of the tobacco h ornworm Manduca sexta. Biosynthesis of LTP, occurrence in hemolymph, a nd the role of LTP-apoproteins in the lipid transfer reaction were inv estigated using antibodies specific for LTP or for each of the apoprot eins. in vitro protein synthesis followed by immunoprecipitation demon strated that LTP is synthesized by the fat body and secreted into the medium. In contrast to apolipophorin Ill, an exchangeable apoprotein o f lipophorin (the major lipid transport protein in hemolymph), apolTP- III could not be detected free in hemolymph. LTP concentrations in the hemolymph were measured by a sandwich EFISA using a mouse monoclonal antibody against apolTP-III as capturing antibody and rabbit polyclona l antibody against apoLTP-I as detecting antibody. LTP concentration i ncreased during the late fifth instar larval stage, followed by a decr ease in the wandering stage. Subsequently, LTP concentrations were str ongly increased in hemolymph of adult moths. The role of the three apo proteins of LTP in the lipid transfer reaction was analyzed using apop rotein-specific antibodies. All three, apolTP-I, -II, and -III, appear ed to be important for lipid transfer activity, as shown by inhibition of lipid transfer by antibodies specific for each of the three apopro teins. (C) 1996 Wiiey-Liss, Inc.