Lipoproteins act as a reusable shuttle for lipid transport in the flying death's-head hawkmoth, Acherontia atropos.
High-density lipophorin (HDLp), the major insect plasma lipoprotein in resting insects, has been postulated to function as a 'reusable shuttle' for lipid transport between tissues, capable of accepting or depositing lipids with maintenance of the structural properties of the particle. Injection of differentially radiolabeled HDLp into resting death's-head hawkmoths revealed that disappearance of the [14C]palmitate labeled lipid component of HDLp (principally diacyglycerol) was relatively quickly (half-life approx. 3 h), whereas turnover time of the apolipoproteins (marked with [14C]protein hydrolysate) was considerably longer (half-life approx. 26 h). These results strongly support the above proposal. To fuel long-distance flight, insects transport lipid in the hemolymph in the form of diacylglycerol-rich low-density lipophorin (LDLp) resulting from a conversion of HDLp to LDLp. By injection of differentially radiolabeled LDLp into flying hawkmoths we demonstrate for the first time in vivo that this mechanism of lipoprotein conversion also functions as a 'reusable shuttle'. While half-life of the lipid moiety of LDLp labeled with [14C]palmitate or [14C]glycerol (mainly diacylglycerol) during flight was only 43 and 94 min, respectively, turnover rate of its apolipoprotein moiety was considerably lower (half-life approx. 30 h). The results demonstrate the unique role of HDLp, i.e., the reversible conversion to LDLp, in lipid delivery to insect flight muscles.
Surholt
B
B
Zoologisches Institut, Universität Münster, Germany.
Goldberg
J
J
Schulz
T K
TK
Beenakkers
A M
AM
Van der Horst
D J
DJ
D000818:Animals; D001692:Biological Transport; D002250:Carbon Radioisotopes; D002352:Carrier Proteins / Q000378:metabolism*; D006458:Hemolymph / Q000378:metabolism; D050356:Lipid Metabolism; D008074:Lipoproteins / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D008297:Male; D009036:Moths / Q000378:metabolism*
D002250:Carbon Radioisotopes; D002352:Carrier Proteins; D008074:Lipoproteins; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; C032830:lipophorin