Plasma Lipoproteins: Structure and Metabolism

Kane, John P.

doi:10.1007/978-1-4684-2832-2_6

Cited by 12 publications

(8 citation statements)

References 274 publications

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“…1, gel D). One of these, which was not always present, had a mobility 1 corresponding to that of the smaller species (apparent Mr 264,000) of apo B seen in chylomicrons; however, its amino acid composition showed it was not the same protein (see below). After separation by preparative gel electrophoresis, all these components of LDL apo B retained their respective electrophoretic mobilities (Fig.…”

Section: Resultsmentioning

confidence: 98%

“…The lipoproteins of human serum contain at least 12 species of proteins' (apolipoproteins) (1). The most abundant of these, apolipoprotein B (apo B) shares with another species, apolipoprotein E, the ability to interact with high-affinity receptors on cell membranes (2).…”

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confidence: 99%

“…apo B is distinguished by its apparent inability to transfer among lipoprotein particles, by its extreme insolubility in aqueous buffers after the lipid moiety is removed, and by its insolubility in 4.2 M tetramethylurea (3). Studies of apo B solubilized with various denaturing solvents and amphiphilic agents have yielded widely varying estimates of molecular weight (1,(4)(5)(6)(7).…”

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confidence: 99%

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Heterogeneity of apolipoprotein B: isolation of a new species from human chylomicrons.

Kane¹,

Hardman²,

Paulus³

1980

Proc. Natl. Acad. Sci. U.S.A.

495

226

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Low density lipoproteins and the triglyceride-rich lipoproteins of human serum each contain proteins of high molecular weight termed apolipoprotein B,which have previously been thought to be identical. We have isolated four species of apolipoprotein B with unique molecular weights and amino acid compositions. We have assigned numerical designations to these species in a centile system based upon their relative apparent Mr in NaDodSO4. One which we term B-100, with an apparent Mr of 549,000 ± 7650 (SD) determined by NaDodSO4 gel electrophoresis, predominates in low density and very low density lipoproteins and is also present in chylomicrons from thoracic duct lymph or from plasma. Substantial amounts of two large proteins designated B-74 (apparent Mr 407,000 ± 5790) and B-26 (apparent Mr 144,500 + 8970), which appear to be complementary fragments or constituents of the B-100 protein, are found in the low density lipoproteins of many individuals. A distinct protein, B-48, with an apparent Mr of 264,000 i 8150 is a major and constant constituent of chylomicrons from thoracic duct lymph or from plasma.The lipoproteins of human serum contain at least 12 species of proteins' (apolipoproteins) (1). The most abundant of these, apolipoprotein B (apo B) shares with another species, apolipoprotein E, the ability to interact with high-affinity receptors on cell membranes (2). apo B is distinguished by its apparent inability to transfer among lipoprotein particles, by its extreme insolubility in aqueous buffers after the lipid moiety is removed, and by its insolubility in 4.2 M tetramethylurea (3). Studies of apo B solubilized with various denaturing solvents and amphiphilic agents have yielded widely varying estimates of molecular weight (1, 4-7).We describe here the presence of four major molecular species of apo B. One of these is nearly the sole form in very low density lipoproteins (VLDL). It also appears in low density lipoproteins (LDL) and chylomicrons from thoracic duct lymph and plasma. Two others appear to be fragments or components of the former and appear only in LDL. The fourth, distinguished by both its molecular weight and amino acid composition, is found only in chylomicrons.MATERIALS AND METHODS Preparation of Lipoproteins. Serum was prepared from blood obtained from donors who had fasted for 12-16 hr. Lipoproteins of serum were separated by repetitive preparative ultracentrifugation in a 40.3 rotor, at 12°C, in a Beckman model L ultracentrifuge (8). VLDL were separated in the p < 1.006 g/cm3 fraction of serum from normolipidemic individuals after centrifugation for 18 hr. The ultracentrifugation was repeated once. Chylomicrons were judged to be absent from preparations of VLDL by the absence of a visible supernatant layer after refrigeration for 24 hr at 40C and by the absence of lipoproteinsThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "ad- Measures to Prevent Nonspecific Degradation of apo B. Gentamycin sulfate, ...

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Section: Resultsmentioning

confidence: 98%

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confidence: 99%

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confidence: 99%

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Heterogeneity of apolipoprotein B: isolation of a new species from human chylomicrons.

Kane¹,

Hardman²,

Paulus³

1980

Proc. Natl. Acad. Sci. U.S.A.

495

226

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“…The bulk of the cholesterol resides in an apolar core in which each sterol molecule is esterified with a long-chain fatty acid. This core of cholesteryl esters is surrounded by a polar coat that contains phospholipid, small amounts of unesterified cholesterol, and a protein called apoprotein B (3). In synthesizing their membranes, cells require unesterified cholesterol.…”

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confidence: 99%

Receptor-mediated endocytosis: insights from the lipoprotein receptor system.

Brown¹,

Goldstein²

1979

Proc. Natl. Acad. Sci. U.S.A.

606

286

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The low density lipoprotein (LDL) receptor system coordinates the metabolism of cholesterol, an essential component of the plasma membrane of all mammalian cells.Studcy of this system has led to an enhanced understanding of the cellular basis of cholesterol homeostasis. It has also brought into focus an important mechanism of metabolic regulationthe process of receptor-mediated endocytosis. In this article, we first describe the receptor-mediated endocytosis of LDL, a sequence of events in which receptor binding and internalization are coupled in specialized regions of the plasma membrane called coated pits. Second, we trace the cellular functions of the cholesterol derived from internalized LDL. Third, genetic evidence is presented to indicate that both the binding and internalization of LDL are mediated by a single receptor molecule that contains two active sites, one mediating binding and the other internalization. Finally, the characteristics of the LDL receptor system are used to suggest models for receptor systems in general. Answers to some of these fundamental questions have recently become available through studies of the lipoprotein receptor system (1, 2). This cell-wide regulatory system coordinates the metabolism of cholesterol, an essential component of the plasma membrane of all mammalian cells. But above and beyond its importance in cholesterol homeostasis, the lipoprotein receptor system has become recognized as a prototype for a mechanism of metabolic regulation-the process of receptor-mediated endocytosis.Before the lipoprotein receptor system is described at the cellular level, a few preliminary comments about cholesterol metabolism seem appropriate. All animal cells require cholesterol for their plasma mrmnbranes, yet the body cannot tolerate excessive cholesterol in blood because the insoluble sterol deposits in artery walls, producing atherosclerosis. Thus, animals have evolved a mechanism for transporting cholesterol through the blood and delivering it to cells, while at the same time avoiding its excessive accumulation. For this purpose, cholesterol is packaged into lipoprotein particles in the liver and intestine, and the soluble lipoproteins are secreted into plasma and carried to target tissues. In man, the most abundant of these particles is low density lipoprotein (LDL).Two-thirds of the cholesterol in human plasma is contained within LDL. The bulk of the cholesterol resides in an apolar core in which each sterol molecule is esterified with a long-chain fatty acid. This core of cholesteryl esters is surrounded by a polar coat that contains phospholipid, small amounts of unesterified cholesterol, and a protein called apoprotein B (3). In synthesizing their membranes, cells require unesterified cholesterol. To use the cholesterol of LDL, cells must be able to take apart the lipoprotein and hydrolyze the cholesteryl esters. This is where the need for multiple subcellular organelles comes in. The key to the process is a cell surface receptor that binds LDL and facilitates its en...

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“…the cow (Bos sp.) and the pig (Sus domesticusl (Osborne and Brewer, 1977 ;Kane, 1977 ;Smith, Pownall and Gotto, 1978 ;Alaupovic, 1980 ;Kane, 1983 (Puppione et al, 1982a ;1982b ;Puppione, 1983) (Puppione et al, 1982a Karlsson (1982) have shown that the major lipoprotein in fetal pig serum, at least until day 90 of gestation, is an LDL-like particle, as judged by its electrophoretic mobility and by immunoassay using an antiserum to adult LDL. Thus, although these authors quote the values as a % of those in adults [adult values : --120 mg/100 ml and -180 mg/100 ml of serum for LDL and HDL, respectively ; Chapman (1980)], calculation showed LDL and HDL levels to be about 80 and 50 mg/100 ml, respectively, in early fetal life (-70 days).…”

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confidence: 99%