Abstract
The diacylglycerol-carrying lipoprotein (DGLP) was purified from hemolymph of the locust, Locusta migratoria, by a rapid method which included a specific precipitation at low ionic concentration and DEAE-cellulose column chromatography. The final preparation was highly homogeneous as judged by gel electrophoresis, electron microscopy, and immunodiffusion. The locust DGLP molecule was almost spherical in shape with a diameter of about 130 A. The molecular weight, determined by a sedimentation equilibrium method, was approximately 580,000. The total lipid content amounted to about 40%. The lipids comprised diacylglycerol (33% of total lipid), hydrocarbon (21%), cholesterol (8%), and phospholipids (36%). The hydrocarbon fraction contained a number of n-alkanes and methylalkanes ranging from C25 to C38 in chain length. Mannose (3%) and glucosamine (0.5%) were associated with the apoprotein of DGLP. Apoprotein of locust DGLP consisted of two subunits, heavy chain (mol wt 250,000) and light chain (mol wt 85,000); carbohydrate (mannose) was associated only with the heavy chain. Tests of physiological function of DGLPs from locust, cockroach, and silkworm suggest that the insect DGLP serves multiple roles as a true carrier molecule in transporting diacylglycerol, cholesterol, and hydrocarbon from sites of storage, absorption, and synthesis to sites where these lipids are utilized as metabolic fuel, precursors for triacylglycerol and phospholipid synthesis, or structural components of cell membrane and cuticle. In addition, the insect DGLPs displayed no species-specificity in terms of the functions, whereas they were immunologically distinguishable.
Highlights
Was purified from hemolymph of the locust, Locustu mzgratoria, by a rapid method which included a specific precipitation at low ionic concentration and DEAE-cellulose column chromatography
Apoprotein of locust DGLP consisted oftwo subunits, heavy chain and light chain; carbohydrate was associatedonly with the heavy chain.m Tests ofphysiological function of DGLPs from locust, cockroach, and silkworm suggest that the insect DGLP serves multiple roles as atruecarrier molecule in transporting diacylglycerol, cholesterol, and hydrocarbon from sitesof storage, absorption, and synthesis tosites where these lipids are utilizedasmetabolic fuel, precursors for triacylglycerol and phospholipid synthesis, or structural components of cell membrane and cuticle
Locusta mzgratoria (2-5 weeks after Lipid extraction, separation, and determination final molt) andadult American cockroaches, Peri-Neutral lipid classes andfree fatty acids were planeta americana, were takenfrom colonies main- extracted from hemolymph, lipoprotein fractions, or tained in this laboratory
Summary
Was purified from hemolymph of the locust, Locustu mzgratoria, by a rapid method which included a specific precipitation at low ionic concentration and DEAE-cellulose column chromatography. It is evident ofDGLP was predominantly associated with diacylfrom our recent report (20) that the second fraction glycerol, andt,hereforet,he efficiency of the is vitellogenin (female-specific protein) that precipi- purification procedure was tested by determining the tates together with DGLP under low ionic concentra- radioactivity of the diacylglycerol fraction recovered demonstrates high homogeneity in terms of molecular shape and size; the molecule is almost globular with a diameter of 131 A f 11.
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