The role of apolipophorin III in in vivo lipoprotein interconversions in adult Manduca sexta

• Published in: The Journal of biological chemistry Vol. 262; no. 9; pp. 4172 - 4176
• Main Authors: Wells, M.A., Ryan, R.O., Kawooya, J.K., Law, J.H.
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 25.03.1987; American Society for Biochemistry and Molecular Biology
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Apolipoproteins - physiology; Biological and medical sciences; Carrier Proteins - metabolism; Chemical Phenomena; Chemistry, Physical; Chromatography, Gel; Diglycerides - metabolism; Fundamental and applied biological sciences. Psychology; Hemolymph - metabolism; Kinetics; Lepidoptera - metabolism; Lipoproteins - metabolism; Lipoproteins, myelin; Male; Manduca sexta; Molecular Weight; Moths - metabolism; Phospholipids - metabolism; Proteins; Sphingidae; Ultracentrifugation; Human; Interconversion; Insecta; Lipids; Lipoprotein; Sphingidae; Metabolism; Arthropoda; Animal; Lepidoptera; Manduca sexta; Adult; Invertebrata; Carrier protein
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)61328-6

Sustained flight in the moth, Manduca sexta, necessitates lipid mobilization and transport to flight muscle, a process mediated by the adipokinetic hormone. An adult specific high density lipophorin (lipoprotein, HDLp-A, Mr = 7.68 × 10(5)) accepts diacylglycerol from the fat body, increasing in size and decreasing in density, to give a low density lipophorin (lipoprotein, LDLp, Mr = 1.56 × 10(6)). During this process, several molecules of the small apolipoprotein, apolipophorin III (apoLp-III), are added to the two molecules originally present in HDLp-A. A study of the time course of adipokinetic hormone-induced loading of diacylglycerol onto HDLp-A, using the analytical ultracentrifuge and gel filtration, suggests that a lipoprotein of density intermediate between HDLp-A and LDLp was formed transiently. Analysis of lipoproteins separated by density gradient ultracentrifugation in the course of the loading process indicates that apoLp-III is added more rapidly than diacylglycerol and that it changes its conformation on the surface as more diacylglycerol is added. Taken together with the known properties of apoLp-III, a prolate ellipsoid with an axial ratio of 3, we suggest that initially apoLp-III adds to the expanded hydrophobic surface of the lipoprotein with its short axis parallel to the surface and that apoLp-III subsequently unfolds to cover a greater area of hydrophobic surface. Exchange experiments with labeled apoLp-III showed that the two apoLp-III molecules in HDLp-A do not exchange with free apoLp-III, even when the lipoprotein passed through a loading and unloading cycle, suggesting a structural role for apoLp-III in HDLp-A.