Isolation and characterization of polymorphic forms of porcine apoC-II by chromatofocusing

Postheparin lipolytic activity in acute and chronic renal failure

Lipid profile and postheparin lipolytic activity (PHLA) were investigated in 21 patients with acute renal failure (ARF), 24 with chronic renal failure (CRF), and 23 healthy volunteers. Plasma triglycerides were significantly elevated in ARF (155.19 +/- 72.39 mg/dL) as well as CRF (166.79 +/- 72.36 mg/dL), as compared to controls (89.91 +/- 23.41 mg/dL, p < .001). PHLA was determined at 5, 10, 30, and 60 min after intravenous heparin (100 U/kg) and was observed to be reduced in ARF (7.82 +/- 1.41 mumol FFA/mL/h) as well as CRF (8.44 +/- 1.68 mumol FFA/mL/h) at 10 min, as compared to the values in the control subjects (12.03 +/- 2.43 mumol FFA/mL/h, p < .01). No correlation was found between PHLA and plasma triglycerides in ARF or CRF. In 15 patients in each group, PHLA subfractions, hepatic triglyceride lipase (HTGL), and lipoprotein lipase (LPL) were determined at similar time intervals after heparin. Both fractions were found to be reduced significantly (p < .01) in ARF as well as in CRF versus controls. These findings indicate that the lipid alterations in acute and chronic renal failure share common features including hypertriglyceridemia and reduced PHLA and its subfractions HTGL and LPL.

Effects of apolipoprotein structure on the kinetics of apolipoprotein transfer between phospholipid vesicles

The kinetics and mechanism of transfer of 14C-labeled human apolipoproteins A-I, A-II and C-III1 between small unilamellar vesicles (SUV) have been investigated. Ion exchange chromatography was used for rapid separation of negatively charged egg phosphatidylcholine (PC)/dicetyl phosphate donor SUV containing bound 14C-labeled apoprotein from neutral egg PC acceptor SUV present in 10-fold molar excess. The transfer kinetics of these apolipoproteins at 37 degrees C are consistent with the existence of fast, slow and apparently 'nontransferrable' pools of SUV-associated lipoprotein: the transfers from these pools occur on timescales of seconds (or less), minutes/hours and days/weeks, respectively. For donor SUV containing about 15 apoprotein molecules per vesicle and at a donor SUV concentration of 0.15 mg phospholipid/ml incubation mixture, the sizes of the fast kinetic pools for apolipoproteins A-I, A-II and C-III1 associated with donor SUV are 2, 10 and 11%, respectively. The sizes of the slow kinetic pools for these apolipoproteins are 16, 71 and 50%, respectively. The transfer of the various apolipoproteins from the slow kinetic pool follows first order kinetics and the half-time (t1/2) values are in the order: apo C-III1 less than apo A-I. Increasing the number of apoprotein molecules per donor SUV enlarges the size of the fast pool and increases the t1/2 of slow transfer. The differences in the kinetics of apolipoprotein transfer between SUV are consequences of the variations in the primary and secondary structures of the apolipoprotein molecules. The slow transfer of apoprotein molecules is mediated by collisions between donor and acceptor SUV; the rate is dependent on the apoprotein molecular weight with larger molecules transferring more slowly from donor SUV containing the same lipid/protein molar ratio. The hydrophobicity of the apoprotein molecule is also significant with less hydrophobic molecules transferring more rapidly. Further understanding of the differences in the kinetics of transfer of these apolipoproteins will require more knowledge of their secondary and tertiary structures.

Comparative molecular properties of swine and human very low density lipoproteins-apoproteins E and C

1. By means of 2-dimensional gradient-gel electrophoresis, the very low density lipoproteins (VLDL) apoproteins E and C profiles from human and swine plasma were studied. 2. The molecular properties (isoelectric point and molecular weight) of the VLDL apoproteins and their isoforms were determined and showed many similarities between species. 3. It also appears evident that a previously unrecognized apoprotein (C-III) and several associated isoforms may exist in swine; however, it's mobility on 2-dimensional gradient gels is very similar to Apo C-II.

Anion-exchange fast protein liquid chromatographic characterization and purification of apolipoproteins A-I, A-II, C-I, C-II, C-III0, C-III1, C-III2 and E from human plasma

This paper describes a procedure for the rapid isolation of urea-soluble apolipoproteins (apo) from delipidated human very-low- and high-density lipoproteins using anion-exchange fast protein liquid chromatography. The separation was complete within 30 min and peaks corresponding to apolipoproteins A-I, A-II, C-I, C-II, C-III0, C-III1, C-III2 and E were identified by comparing their chromatographic, electrophoretic and immunological behaviour with that of purified standards of each protein. A second purification step is necessary to obtain pure apolipoproteins. Apo E, which is difficult to purify by conventional chromatography, has been obtained in a good yield. The apo C-II that was obtained produced a symmetrical peak on chromatography but three bands in isoelectric focusing. The method can be upgraded to a preparative scale and offers the possibility of direct purification of apolipoproteins both from high-density lipoproteins and (following preliminary gel chromatography) from very-low-density lipoproteins.

Purification of biologically active apolipoproteins by chromatofocussing

Chromatofocussing has been used to isolate homogeneous apolipoproteins (apo) from human very-low-density lipoproteins and high-density lipoproteins with protein recovery of 70%. The inclusion of sulfhydryl-reducing agent (dithiothreitol) was required during solubilization of the lipoproteins (following delipidation) to achieve reproducible elution profiles. Removal of polyvalent buffers from apoproteins was rapidly accomplished on small columns of hydroxylapatite. The biological activity of purified apo AI and apo CII was confirmed by assessment of their ability to activate lecithin:cholesterol acyltransferase or lipoprotein lipase, respectively. Functional properties of isolated apo E were assessed by in vitro interaction with the low-density lipoprotein receptor expressed by cultured fibroblasts. Apolipoproteins purified by this rapid procedure exhibit identical physical, chemical and biological properties to those purified by other, more tedious techniques.

Human apolipoprotein C-II quantitation by sandwich enzyme-linked immunosorbent assay

A specific, sensitive and accurate, non competitive enzyme-linked immunosorbent assay was developed for the quantitation of human apolipoprotein C-II. Using apolipoprotein C-II and apolipoprotein C-III immunosorbent columns, monospecific anti-apolipoprotein C-II antibodies were prepared for coating and for the preparation of a peroxidase-antibody conjugate. The assay is sensitive down to 0.25 ng apolipoprotein C-II per assay and precise, with mean intra- and inter-assay coefficients of variation of 3.1% and 7.9% respectively. The apolipoprotein C-II concentrations in normolipaemic and hyperlipaemic plasma were not affected by delipidation, and increased only slightly after treatment with detergents or urea. The mean plasma apolipoprotein C-II concentration in a group of 30 normolipaemic subjects, was 33.1 +/- 7.5 mg/l. All hypertriglyceridaemic subjects had significantly elevated apolipoprotein C-II plasma concentrations, which were most pronounced in Fredrickson type III and type V patients. The apolipoprotein C-II profiles, obtained by column fractionation of 6 normolipaemic and 11 hypertriglyceridaemic plasmas, demonstrated a shift of apolipoprotein C-II towards the triglyceride-rich lipoproteins in hypertriglyceridaemic subjects.

Isolation and properties of porcine lecithin:cholesterol acyltransferase

Lecithin: cholesterol acyltransferase (LCAT, phosphatidylcholine: sterol O-acyltransferase, EC 2.3.1.43) was purified approximately 20 000-fold from pig plasma by ultracentrifugation, phenyl-Sepharose and hydroxyapatite chromatography. Purified LCAT had an apparent relative molecular mass of 69 000 +/- 2000. By isoelectrofocusing it separated into five or six bands with pI values ranging from pH 4.9 to 5.2. The amino acid composition was similar to that of the human enzyme. An antibody against pig LCAT was prepared in goat. The antibody reacted against pig LCAT and gave a reaction of partial identity with human LCAT. Incubation of pig plasma or purified enzyme with the antibody virtually inhibited LCAT activity. The same amount of antibody inactivated only 62% of the LCAT activity in human serum. Pig and human LCAT were activated to the same extent by either human or pig apolipoprotein A-I (apo-A-I) using small liposomes as substrate. Human apoA-I, however, caused a higher esterification rate for both enzymes. Using apoA-I and small liposomes as a substrate, the addition of apoC-II up to 4 micrograms/ml had no effect on the LCAT reaction, but above this concentration LCAT was inhibited. Small liposomes with phosphatidylcholine/cholesterol molar ratios of 3:1 up to 8.4:1 did not show any significant differences in the LCAT reaction, when used as substrates in the presence of various amounts of apoA-I and albumin. In contrast, the LCAT activity was significantly reduced by liposomes with phosphatidylcholine/cholesterol molar ratios below 3:1.

Fast protein chromatofocusing of human very-low-density lipoproteins

Using fast protein chromatofocusing, a high-efficiency column chromatography method with a self-generated pH gradient and focusing effects, soluble human very-low-density lipoprotein (VLDL) apolipoproteins were fractionated between pH 6.3 and 4.0. In the presence of 6 mol/l urea and with a flow rate of 1 ml/min, one run (up to 10 mg of protein) took 30 min. VLDL apolipoproteins were separated in seven peaks. As revealed by SDS-polyacrylamide gel electrophoresis, isoelectric focusing and double-immunodiffusion against mono-specific antisera, fractions corresponded to the following proteins: apolipoprotein C-I, albumin, apolipoproteins A-I, E, C-II plus C-III0, C-III1 and C-III2, respectively. Apolipoproteins were eluted in sharp, well-resolved peaks. The recovery of proteins was 78% of the starting material. With fast protein chromatofocusing, an efficient isolation of single apolipoproteins is possible from small amounts of VLDL apolipoprotein preparations. This technique is superior to the commonly used, time-consuming methods for apolipoprotein isolation.

Chromatofocusing of apolipoproteins from human serum high density lipoprotein

Human HDL was delipidated and the apolipoproteins were fractionated by chromatofocusing. Chromatofocusing, which separates proteins due to their differing isoelectric points, resulted in 8 peaks with corresponding pI values of 7.40, 6.92, 6.64, 5.48, 5.30, 5.18, 4.92 and 4.63. By one single chromatofocusing run four apolipoproteins were obtained in pure form. Two additional polypeptides could be purified during the desalting step using phenyl-Sepharose.