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Biomedical subjects

R L Jackson

Publications and source records attributed to R L Jackson.

At least 217 records · Page 12Linked to original sources
PubMed1977

Primary structure of very low density apolipoprotein C-II of human plasma.

Apolipoprotein C-II (apoC-II), a protein constituent of very low density lipoproteins of human plasma and the activator protein of lipoprotein lipase, has been isolated and its amino acid sequence has been studied. The protein has 78 amino acid residues and is lacking cysteine, cystine, and histidine. Chromatography on Bio-Gel P-30 in 25% formic acid of the cyanogen bromide digest of apoC-II yields three fragments designated as CNBr-I, -II, and -III. They contained 50, 19, and 9 residues, respectively. The alignment of the cyanogen bromide fragments has been established as CNBr-III-I-II by isolation and sequence of the tryptic peptides of the intact protein. The amino acid sequences of the tryptic and CNBr peptides were determined by conventional methods. With this information, it was possible to establish the complete amino acid sequence of apoC-II.

Amino Acid Sequence↗
PubMed1977

Quantification of apolipoprotein B in grossly normal human aorta.

A quantitiative electroimmunodiffusion (EID) assay was developed for apolipoprotein B (apoB), the major apoprotein of human plasma low density lipoproteins (LDL) and very low density lipoproteins (VLDL). Specificity, sensitivity (30-200 ng) and reproducibility (11%) were established. We used this system to determine the amount of buffer-soluble apoB in supernatant fractions from homogenates of the intima from grossly normal human aortas. Assays of whole tissue minces yielded only one-third of the apoB in supernatant fractions. Intimal homogenates contained 0.34-18.45 mug of apoB/mg of tissue, dry weight (mean 5.42 +/- 3.95 SD). We also found that no apoB was detected in the homogenates of adjacent tunica media. Furthermore, most of the intimal apoB was found in the LDL density (d) fraction (d 1.006-1.063) after differential ultracentrifugation, while the VLDL (d less than 1.006) fraction contained only negligible amounts of apoB. By electron microscopy, it was determined that the LDL density fraction contained particles 200-250 A in diameter which were similar in size to plasma LDL. These results suggest that grossly normal aortas contain significant quantities of intact LDL.

Adolescent↗
PubMed1977

Female steroid hormones and lipoprotein synthesis in the cockerel: effects of progesterone and nafoxidine on the estrogenic stimulation of very low density lipoproteins (VLDL) synthesis.

Since progesterone is known to modulate the effects of estradiol in a number of organ systems, we have studied the effects of the two hormones on very low density lipoproteins (VLDL) synthesis in the cockerel. We have also examined the effect of an estrogen antagonist, nafoxidine-HCl, on the process. When three week-old cockerels were treated with a single injection of estradiol (1 mg) or estradiol (1 mg) + progesterone (2 mg), plasma VLDL increased within 5 h, reached a peak at 48 h and returned to baseline values at 68 h. There was no significant difference between estradiol or estradiol + progesterone treated animals. Liver slices were prepared from similarly treated animals and incubated in vitro with L-[3H]lysine for 2 h. Following homogenization and centrifugation at 105,000 X g, newly synthesized VLDL were quantitiated in the supernatant fluid by immunoprecipitation with a monospecific antibody. Radioactivity incorporated into VLDL was found to increase from low baseline levels to a peak at about 17 h after treatment. There was, again, no significant difference between estradiol and estradiol + progesterone-treated animals. Estrogen priming or progesterone pretreatment also did not significantly alter the VLDL biosynthetic response in liver slices to estradiol alone or in combination with progesterone. When the estrogen-antagonist nafoxidine-HCl (5 mg) was administered simultaneously with estradiol (1 mg), it totally inhibited the VLDL biosynthetic response in liver slices in vitro. The interaction of estradio, progesterone and nafoxidine-HCl on the hepatic synthesis of VLDL should serve as a valuable model for the study of VLDL synthesis and its regulation as well as the mode of action of the sex steroid hormones in the liver.

Animals↗
PubMed1977

Estrogen induction of plasma vitellogenin in the cockerel: studies with a phosvitin antibody.

The effects of estrogen on plasma vitellogenin have been studied in the cockerel by immunoprecipitation techniques using an antiserum prepared against the egg yolk phosphoprotein, phosvitin. The antiserum gave precipitin lines of complete identity to phosvitin and to vitellogenin which was isolated from hen plasma by DEAE-cellulose chromatography and by affinity chromatography using anti-phosvitin coupled to Sepharose 4B. The cross-reactivity of vitellogenin and phosvitin adds support to the concept that plasma vitellogenin is the precursor phosphoprotein of egg yolk phosvitin. In the three-week old cockerel, anti-phosvitin produced no detectable immunoprecipitate in the plasma. However, after a single sc injection of diethylstilbestrol (2.5 mg), plasma vitellogenin levels began to increase at 4 h and reached a maximum 20-30 h after hormone administration. The increase in plasma levels of triglyceride paralleled those of vitellogenin. These studies suggest that there is no significant time lag in the estrogenic induction of plasma vitellogenesis in the cockerel, the longer lag periods observed by other investigators may be a function of the sensitivity of the assays used for detecting vitellogenin.

Amino Acids↗
PubMed1977

Influence of dietary trans-fatty acids on swine lipoprotein composition and structure.

Four groups of 20 weanling swine each were fed either (a) basal diet, (b) basal plus hydrogenated fat (13% trans), (c) basal plus hydrogenated fat (13% trans) and 0.4% cholesterol, or (d) basal plus beef tallow (all cis). After six months of feeding, the animals were killed and the blood and aortas were removed. Very low density, low density, and high density lipoproteins were then isolated from the plasma by ultracentrifugal flotation. Although the fatty acid composition of the basal diet was different from the diets supplemented with either hydrogenated fat containing trans-fatty acid or beef tallow containing all cis, the lipid and fatty acid compositions of each of the isolated lipoprotein classes for the four groups of animals were remarkably similar. Elaidate was clearly incorporated into the lipoproteins of animals fed hydrogenated fat, but the level of incorporation was generally less than 5%. In a direct comparison of the structure of the lipoproteins from the different groups, we did not find any significant differences in their physical properties as determined by pyrene fluorescence and electron paramagnetic resonance methods. Grossly visible fatty streaks and fibrous plaques were not found in any of the swine aorta. However, light and electron microscopy indicated the presence of atherosclerotic lesions in the distal abdominal aorta and bifurcation. These studies demonstrate that a diet containing a substantial amount of trans-fatty acid leads to a small but definite incorporation into the swine lipoproteins. However, such changes had relatively little effect on lipoprotein structure or the presence of atherosclerotic lesions in these 6-month-old swine.

Animals↗
PubMed1976

Amyloid A: amphipathic helixes and lipid binding.

Polypeptide segments, composed of alpha helixes with specific surface topography termed amphipathic helixes, have been proposed as the basic lipid-associating domains of apolipoproteins from the plasma lipoproteins. A computer search for proteins having sequences that could form amphipathic helixes indicated that amyloid A, a pathologically occurring protein usually associated with "secondary" amyloidosis, also contained amphipathic helixes. In studies reported here, amyloid A is shown to associate spontaneously with phospholipid vesicles with the following results: (a) the formation of a protein-lipid complex isolated by equilibrium density gradient ultracentrifugation, (b) a 100% increase in alpha helicity as measured by circular dichroism, (c) a 9-nm shift in the fluorescence maximum due to the single tryptophan residue located in the amphipathic region, indicating the tryptophan is moving from a polar to a nonpolar environment, and (d) the formation of stacked disk-like protein-lipid complexes as visualized by negative stain electron microscopy. The temperature dependence of the circular dichroic spectrum of the amyloid A-phospholipid complex suggests that the complex is formed by insertion of protein between the fatty acyl chains of the lipid. These findings suggest that the amphipathic helix is an important structural unit in lipid-associating proteins and that this unit can be recognized on the basis of its amino acid sequence. In addition, these studies have implications for the origin and function of amyloid A protein.

Amyloid↗
PubMed1976

Isolation and characterization of the major apolipoprotein from chicken high density lipoproteins.

High density lipoproteins were isolated from plasma of white Leghorn hens by ultracentrifugal flotation between densities 1.063 and 1.210 g/ml. After delipidation, the lipid-free proteins were fractionated by chromatography on Sephadex G-150 in urea; one major apolipoprotein was isolated and characterized. From its chemical, physical and immunochemical properties, the major apoprotein from hen high-density lipoproteins has characteristics similar to the major apoprotein of human high density lipoproteins, apoA-I. Thus the hen protein has been designated hen apoA-I. Hen apoA-I has a molecular weight of approximately 28 000 as determined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Its calculated molecular weight from its 234 constituent amino acids is 26 674. Hen apoA-I differed from its human counterpart by containing isoleucine. Treatment of hen apoA-I with carboxypeptidase A yielded a COOH-terminal sequence of Leu-Val-Ala-Gln. Automatic Edman degradation of the apoprotein gave an NH2-terminal sequence of Asp-Glu-Pro-Gln-Pro-Glu-Leu. Hen apoA-I had a circular dichroic spectrum typical of alpha-helical structures; the calculated helicity was 90%. Goat antisera prepared to hen apoA-I formed precipitin lines of complete identity to the hen apoprotein but lines of only partial identity to human apoA-I. These studies show that the major apoprotein from hen and human high-density lipoproteins have similar properties to each other suggesting a common physiologic function.

Amino Acid Sequence↗
PubMed1976

Apo-lipoprotein localization in human atherosclerotic arteries.

A study documenting the localization in human arteries of apoproteins from human plasma high density (HDL, low density (LDL), and very low density (VLDL) lipoproteins was undertaken in light of their possible roles in the pathogenesis and regression of the atherosclerotic process in man. Apo A-I from HDL, apo B from LDL, apo C-III from VLDL were all localized by immunohistochemical techniques to generally the same areas of athersclerotic lesions. These consisted of certain bands of collagen and elastic fibers in fatty streaks and fibrous plaques, and extracellular pools of neutral lipid in fibrous plaques. Apoproteins were also occasionally present in areas of diffuse intimal thickening in coronary arteries. Extensiveness and frequency of appearance of apo B in atherosclerotic lesions was greatest in type II hyperlipoproteinemics, thus correlating with the plasma apo B levels. Employing an immuno-peroxidase procedure, apo B was localized ultrastructurally in atherosclerotic lesions to the outer surface of spheres ranging in diameter between 250 and 700 A. These spheres, localized predominantly in lipid cores and between collagen bands, were also seen in negatively-stained preparations of arterial extracts which also reacted positively against anti-apo B, SUGGESTING THAT THE SPHERES MAY REPRESENT NATIVE LDL and VLDL. The superimposed localization of apo A-I, apo B, and apo C-III in atherosclerotic lesions suggests that a specific interaction exists between certain lesion components and these apoproteins.

Apoproteins↗
PubMed1976

Synthesis of very low density lipoproteins in the cockerel. Effects of estrogen.

The effect of estrogen on the synthesis of plasma very low density lipoproteins (VLDL) in the cockerel was studied both in vivo and in vitro. Synthesis was studied by immunoprecipitation techniques with antisera prepared against VLDL and a major VLDL protein. VLDL were isolated from the plasma of white Leghorn hens and estrogen-treated white Leghorn cockerels by ultracentrifugal flotation at d 1.006 g/ml. After delipidation, the lipid-free proteins (apoproteins) were fractionated on Sephadex G-150 and DEAE-cellulose. Both the hen and the estrogen-treated cockerel VLDL were shown to contain an identical apoprotein with a mol wt of approximately 12,000; the apoprotein is designated fraction B. Reduction and S-carboxy-methylation of fraction B resulted in a reduction of the molecular weight by approximately one-half, indicating a dimer-monomer relationship. Antiserum prepared to the hen VLDL dimer protein gave precipitin lines of complete identity to both the hen and cockerel dimer, monomer, VLDL, apoVLDL, low density lipoproteins, and plasma; no precipitin line was formed with either hen or cockerel high density lipoproteins. After a single subcutaneous injection of diethylstilbestrol into the cockerel, plasma VLDL protein, cholesterol, and triglyceride increased, reaching a maximum 24--48 h after hormone administration. Liver slices from similarly treated animals were incubated in vitro in culture medium in the presence of [3H]lysine for 2 h. Immunoprecipitable radioactivity in VLDL increased within 2 h of diethylstilbestrol treatment and reached a maximum at 24 h; VLDL radioactivity returned to base-line levels by 72 h. At the peak of induction, newly synthesized VLDL represented 11% of the total soluble protein synthesized. When actinomycin-D (5 mg/kg) was administered simultaneously with estrogen, the induction of VLDL synthesis was totally inhibited. To determine whether the effect of estrogen on VLDL synthesis was mediated at the level of transcription, partially-purified cockerel liver mRNA was prepared from estrogen-treated animals and the mRNA activity for fraction B was quantitated in a wheat germ translation system. Fraction B mRNA was found to increase from a low base-line value to a maximum 16-24 h after estrogen treatment, returning towards baseline values at 30 h. At the peak of induction, fraction B constituted 12% of the total protein synthesized. The kinetics of induction of fraction B mRNA activity in the cell-free translation system is very similar to that observed in liver slice experiments. This finding suggests that estrogen stimulates VLDL synthesis, at least partially, by enhancing the accumulation of the mRNA for one of their major apoproteins.

Animals↗
PubMed1975

A comparative study on the removal of cellular lipids from Landschütz ascites cells by human plasma apolipoproteins.

The effects of human plasma lipoprotein-proteins on the removal of cellular lipids from Landschütz ascites cells were studied. Cellular lipids were labeled by injecting mice previously injected with ascites with either [3H]cholesterol or [3H]choline. Apoproteins from very low density (apoC-I, C-II, and C-111) and high density (apoA-I and A-II) lipoproteins were used. Each of the apoproteins alone was ineffective in removing cellular [3H]cholesterol. However, when synthetic phosphatidylcholines of known composition were added to each apoprotein and the experiments were repeated using either apoprotein-lipid mixtures or ultracentrifugally isolated complexes, the removal of sterol was considerably enhanced. Complexes of saturated phosphatidylcholines with apoA-II, apoC-I, or apoC-III were the most effective in releasing cellular sterol. Apoprotein-phospholipid complexes were much less effective in removing cellular [3H]phosphatidylcholine than the free apoproteins; apoA-I and apoC-I were the best of the five apoproteins studied. When a comparison was made of the adsorption of iodinated apoproteins to ascites cells, 3 to 4 times more apoA-II and apoC-III were bound than apoA-I. The binding of apoproteins was time and temperature dependent. Approximately 50% of the radioactivity that remained in the washed cells was removed with trypsin. To determine if the counts remaining in the trypsin-treated cells were internalized, identical experiments were performed using human erythrocytes, cells that do not exhibit pinocytosis. Again, approximately 50% of the radioactivity of the iodinated apoproteins was not released by trypsin. Succinylation of apoA-II not only destroys its phospholipid-binding properties but also its adsorption to red cells. These results suggest that the plasma apoproteins differ in their ability to remove cellular lipids and bind to both ascites and red cell membranes, and possibly to specific phospholipids, in such a way that only a part of the apoprotein is degraded with proteases.

Apoproteins↗
PubMed1975

The interaction of human plasma glycoaminoglycans with plasma lipoproteins.

Modifications of existing methods have allowed for the isolation and purification of various species of plasma glycosaminoglycans on the basis of their sulfate content and molecular size. All of the preparations precipitated human plasma low density lipoproteins (LDL); maximal precipitation occurred with amounts of glycans corresponding to 50 mug of hexuronate and 12 mg of LDL. The interaction of glycans with pyrene-labeled lipoproteins was also studied, measuring variations of the fluorescence emitted by the monomer (M) and excimer (E) species of the bound pyrene. The ratio IE/IM is proportional to c/eta, where c is the microscopic concentration of the pyrene confined to the hydrocarbon region of the lipoprotein and eta is the microviscosity of that region. To 0.12 mg of pyrene-labeled LDL, very low density lipoproteins (VLDL) or high density lipoproteins (HDL) were added increasing amounts of the various glycan preparations. The sulfate-rich species decreased the IE/IM ratio of LDL and HDL but not that of VLDL. This finding suggests that the glycan caused a change in lipoprotein conformation associated with either an increased volume or increased microscopic viscosity of the hydrocarbon region. The modification of LDL conformation could be prevented by proteolytic treatment of the sulfate-rich species or by addition to the system of suitable amounts of sulfate-poor species or of chrondroitin-4-sulfate, but could not be prevented by increased ionic concentration. These results suggest that the two main species of plasma glycans are important in maintaining adequate rheological properties of plasma lipoproteins.

Chondroitin↗
PubMed1975

Effect of the human plasma apolipoproteins and phosphatidylcholine acyl donor on the activity of lecithin: cholesterol acyltransferase.

The human plasma apoproteins apoA-I and apoC-I enhanced the activity of partially purified lecithin: cholesterol acyltransferase five to tenfold with chemically defined phosphatidylcholine:cholesterol single bilayer vesicles as substrates. By contrast, apoproteins apoA-II, apoC-II, and apoC-III did not give any enhancement of enzyme activity. The activation by apoA-I and apoC-I differed, depending upon the nature of the hydrocarbon chains of phosphatidylcholine acyl donor. ApoA-I was most effective with a phosphatidylcholine containing an unsaturated fatty acyl chain. ApoC-I activated LCAT to the same extent with both saturated and unsaturated phosphatidylcholine substrates. Two of the four peptides obtained by cyanogen bromide cleavage of apoA-I retained some ability to activate LCAT. The efficacy of each of these peptides was approximately 25% that of the whole protein. Cyanogen bromide fragments of apoC-I were inactive. The apoproteins from HDL, HDL2, and HDL3, at low protein concentrations, were equally effective as activators of LCATand less effective than apoA-I. Higher concentrations of apoHDL, apoHDL2, and apoHDL3 inhibited LCAT activity. ApoC and apoA-II were both found to inhibit the activation of LCAT by apoA-I. The inhibition of LCAT by higher concentrations of apoHDL was not correlated with the aopA-II and apoC content.

Acyltransferases↗
PubMed1975

The primary structure of human plasma high density apolipoprotein glutamine I (ApoA-I). I. The amino acid sequence of cyanogen bromide fragment II.

Apolipoprotein glutamine I (apoLP-Gln-I or apoA-I) is one of the major protein constituents of human plasma high density lipoproteins. The protein has 245 amino acid residues, including 3 residues of methionine, and is lacking isoleucine, cystine, and cysteine. Cleavage of apoLP-Gln-I with cyanogen bromide yields four fragments, designated in their order of elution from Bio-Gel P-30 as CNBr I, II, III, and IV. In the present study, we report the complete amino acid sequence of the NH2-terminal fragment, CNBr II, a peptide that contains 90 amino acid residues.

Amino Acid Sequence↗