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J Ihm

Publications and source records attributed to J Ihm.

32 records · Page 2Linked to original sources
PubMed1986

Ihm responds.

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Journal Article↗
PubMed1986

Immunoaffinity purification of the lipid transfer protein complex directly from human plasma.

The human cholesteryl ester (CE) and triglyceride (TG) exchange protein (denoted LTC or lipid transfer complex) was isolated in a single step from plasma using immunoaffinity batch extraction. Antibodies were raised against two preparations of conventionally purified LTC. LTC-I and LTC-II (purified 20,000-fold and 3500-fold, respectively) were used as immunogens. The antiLTC antibodies were isolated by anion-exchange chromatography and coupled to Affi-Gel 10. Chromatography of plasma on antiLTC Affi-Gel removed all of the CE and TG transfer activity. Moreover, LTC prepared from both antiLTC-I and antiLTC-II-Affi-Gel matrices were identical when analyzed by sodium dodecyl sulfate-polyacrylamide gel LTC electrophoresis. LTC exhibited two protein bands of Mr (apparent) 67,000 and 58,000 and a broad, faintly staining region at greater than 150,000. Analysis of LTC by immunoblotting indicated that both antiLTC-I and antiLTC-II antibodies recognized the same LTC proteins. Isoelectric focussing of LTC gave two pI values, 5.2 and 8.7. These data suggest that LTC is a complex of specific proteins and perhaps lipid. Specific CE and TG exchange activities of immunoaffinity-purified LTC were comparable, although the activities were low with respect to that of the antigen used to generate antiLTC-I. This is not due to contamination of LTC by albumin, lecithin:cholesterol acyltransferase, or apolipoproteins AI, AII, B, CIII, D, or E.

Adult↗
PubMed1982

Interaction of a human plasma lipid transfer protein complex with lipid monolayers.

The interaction of a purified human plasma lipid transfer complex with cholesteryl ester, triacylglycerol and phosphatidylcholine in binary and ternary lipid monolayers was investigated. The lipid transfer complex, designated LTC, catalyzes the removal of cholesteryl oleate and triacylglycerol from phosphatidylcholine monolayers. Preincubation of LTC with p-chloromercuriphenyl sulfonate inhibits LTC-catalyzed removal of triacylglycerol; cholesteryl ester removal is not affected. The rate of LTC-facilitated removal of cholesteryl oleate from a phosphatidylcholine monolayer depends on the amount of LTC added to the subphase up to 100 micrograms protein. In addition, the rate of the LTC-catalyzed transfer of cholesteryl oleate to the subphase increases linearly as the amount of cholesteryl oleate in the monolayer increases to 6 mol%. LTC also removes cholesterol from phosphatidylcholine-cholesterol monolayers, albeit at a rate which is 15% of that for removal of cholesteryl oleate. The ability of LTC to facilitate triacylglycerol and cholesteryl ester removal depends on the composition of the monolayer. Phosphatidylcholine supports cholesteryl ester transfer whereas sphingomyelin-cholesteryl ester monolayers are almost refractory to LTC. In contrast, LTC removes triacylglycerol from either a phosphatidylcholine or a sphingomyelin monolayer. The results suggest the existence of at least two lipid transfer proteins, one of which catalyzes the removal of cholesteryl ester and the other triacylglycerol. The role of these proteins as they relate to lipoprotein metabolism is discussed.

Carrier Proteins↗
PubMed1982

Plasma protein-facilitated coupled exchange of phosphatidylcholine and cholesteryl ester in the absence of cholesterol esterification.

A protein(s) which catalyzes the exchange of phosphatidylcholine and cholesteryl ester between plasma lipoproteins has been purified 10,000-fold from lipoprotein-free human plasma. The apparent molecular weight of the protein of the active fraction, designated lipid transfer complex (LTC), is approximately 61,000; when electrophoresed in 6 M urea, 0.1% sodium dodecyl sulfate on a 3-20% polyacrylamide gradient, the protein appears as a doublet of molecular weights 58,000 and 63,000. The active material is a glycoprotein which binds to concanavalin A. Human LTC is a lipid-protein complex with phospholipid, cholesterol, cholesteryl ester, and glyceride comprising 7% of the total mass. A similar glycoprotein (or glycoproteins) exists in rat plasma, although the fold-purification thus far achieved is low: about 500-fold. Moreover, the rat preparation enhances exchange of phosphatidylcholine, but does not appreciably enhance exchange of cholesteryl ester. Partially purified LTC (less than or equal to 3500-fold) exists in a complex with lecithin: cholesterol acyltransferase. Active lecithin: cholesterol acyltransferase is not, however, required for exchange of phosphatidylcholine or cholesteryl ester facilitated by human LTC. The rates of exchange of phosphatidylcholine and cholesteryl ester facilitated by human LTC are equal. Coupled lipid exchange occurs at all stages of LTC purification, at values of pH between 5 and 10, and at ionic strengths as great as 0.9. Moreover, phosphatidylcholine and cholesteryl ester are exchanged with 1:1 stoichiometry in the presence of thiol group reagents such as 5,5'-dithiobis-(2-nitrobenzoic acid). Both lipid exchange activities are relatively resistant to elevated temperatures. Coupled exchange of phospholipid and neutral lipid is not dictated by the nature of the lipoprotein donor and acceptor substrates: bovine liver phospholipid exchange protein catalyzes exchange of phosphatidylcholine but not cholesteryl ester between low and high density lipoproteins under conditions identical with those in which human LTC facilitates exchange of both lipids.

Animals↗
PubMed1982

Kinetics of plasma protein-catalyzed exchange of phosphatidylcholine and cholesteryl ester between plasma lipoproteins.

A lipid transfer complex (LTC) isolated from human plasma catalyzes equimolar exchange of cholesteryl ester and phosphatidylcholine between low density (LDL) and high density (HDL) plasma lipoproteins. Activation parameters for LTC-catalyzed exchange of neutral and polar lipid are equal and are not influenced by the degree of purity of the catalyst. Activation parameters for exchange of both cholesteryl ester and phosphatidylcholine are influenced by the extent of saturation of phosphatidylcholine fatty acyl groups. The activation parameters also depend on the amount of HDL present in the assay. The flux rates of lipid exchange depend on the concentration of both LDL and HDL. At constant HDL concentration, flux rates become independent of LDL concentration when the ratio of [LDL]:[HDL] exceeds 9:1 (based on cholesteryl ester); at constant LDL concentration, facilitated LDL,HDL lipid exchange is inhibited at high HDL concentration, suggesting preferential HDL,HDL exchange. Analysis of the dependence of initial lipid exchange rate on LDL concentration at two constant HDL concentrations suggests that, in the reaction pathway, LTC mediates a productive collision (ternary complex) between LDL and HDL. A kinetic mechanism consistent with the data is one in which lipid exchange occurs in a ternary complex consisting of LTC, HDL and LDL. At low HDL concentration, this complex is formed by a random sequential route; at high HDL concentration, the mechanism is ordered sequential since the reactants are an LTC-HDL complex and LDL.

Carrier Proteins↗
PubMed1978

Transfer of phosphatidylcholine facilitated by a component of human plasma.

A constituent of lipoprotein-free (p greater than 1.21) human plasma from normolipemic donors facilitates the transfer of diacyl phosphatidylcholine from unilamellar egg yolk phosphatidylcholine liposomes to liver mitochondria. The active component is heat labile, has a hydrated density greater than 1.25 and an apparent molecular weight of more than 100 000. The presence of this protein in plasma may facilitate movement of diacylphospholipids between the surfaces of lipid-containing particles such as lipoproteins and erythrocytes. Knowledge of the properties and behavior of this protein are important in designing methods of drug therapy based on encapsulation in biodegradable lipid vesicles.

Carrier Proteins↗