Selective labelling of apolipoproteins A-I and C-I at methionine residues by (3H) methyl exchange

Apolipoproteins C-I and A-I were radioactively labelled with tritium by (3H)-methyl exchange. The methionine residues were first methylated with (3H)-methyl iodide at pH 4 and the reaction products were purified by gel filtration and cation exchange chromatography. The products were then demethylated with 2-mercaptoethanol (6 M) at pH 8.6 to regenerate the apolipoproteins in an unmodified but tritiated form. The specific radioactivity for apolipoprotein C-I and A-I was 3.5 X 10(6) and 1.5 X 10(7) dpm/pmol respectively. The properties of (3H)-apolipoprotein C-I were examined by reversed phase HPLC and by incorporation into very low density lipoproteins (VLDL).     

Immunoaffinity isolation of apolipoprotein E-containing lipoproteins

Discrete apolipoprotein E-containing lipoproteins can be identified when EDTA plasma is fractionated on columns of 4% agarose. The present study has demonstrated, by physical and metabolic criteria, that these apolipoprotein E-containing lipoprotein subclasses may be further isolated by immunoaffinity chromatography. Whole plasma was first bound to an anti-apolipoprotein E immunoadsorbent prior to gel filtration on 4% agarose. After elution from the affinity column and dialysis, the bound fraction was chromatographed on 4% agarose. Discrete subfractions of apolipoprotein E could be demonstrated within elution volumes similar to those observed in the original plasma. When whole plasma was first submitted to gel filtration and the apolipoprotein E-containing lipoproteins of either intermediate- or of high-density lipoprotein (HDL) size were subsequently bound to anti-apolipoprotein E columns, the bound eluted fractions maintained their size and physical properties as shown by electron microscopy and by rechromatography on columns of 4% agarose. The metabolic integrity of apolipoprotein E-containing very-low-density lipoproteins (VLDL) was examined by coinjection into a cynomolgus monkey of 125I-labeled apolipoprotein E-rich and 131I-labeled apolipoprotein E-deficient human VLDL which had been separated by immunoaffinity chromatography. The plasma specific activity time curves of the apolipoprotein B in VLDL, intermediate-density (IDL) and low-density (LDL) lipoproteins demonstrated rates of decay and precursor-product relationships similar to those obtained after injection of whole labeled VLDL, supporting the metabolic integrity of VLDL isolated by immunoaffinity chromatography.     

Isolation of a low molecular mass vasoactive intestinal peptide binding protein.

A vasoactive intestinal peptide (VIP) binding protein was purified in active form by detergent solubilization of lung membranes, gel filtration, VIP-Sepharose affinity chromatography, reverse phase high performance liquid chromatography, and anion exchange chromatography. The mass of this protein was estimated at 18 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and 17 kDa by gel filtration. The binding of VIP by this protein was inhibited by Mg2+, covalent cross-linking of [Tyr10-125I]VIP to the protein produced two radioactive bands at 22 and 26 kDa identified by electrophoresis, and the purified protein exhibited saturable and high affinity binding of VIP and the related neuropeptide, rat growth hormone releasing factor.     

Purification and characterization of recombinant human interleukin-1 beta produced in Escherichia coli

Recombinant human interleukin-1 beta (rIL-1 beta) produced in Escherichia coli was purified to homogeneity by a combination of mass ion exchange column chromatography, ion exchange and gel filtration high performance liquid chromatography. The purified rIL-1 beta had a molecular weight of 18 kD on SDS-polyacrylamide gel electrophoresis and an isoelectric point of 6.9 on analytical isoelectric focusing. These values were almost same as those of natural interleukin-1 beta. The amino acid composition and amino acid sequence of the amino terminal region were consistent with those deduced from the cDNA sequence. In addition, the primary structure was confirmed by peptide mapping with lysyl-endopeptidase on reverse phase HPLC. Besides rIL-1 beta with amino terminal Ala, two molecular species, [Met0] rIL-1 beta and [desAla1] rIL-1 beta, were also obtained. Biological and physicochemical properties of the three species of rIL-1 beta were compared.     

Isolation of subfractions of human very low density lipoproteins by zonal ultracentrifugation.

Very low density lipoproteins (VLDL) have been isolated and subfractionated on the basis of their differing flotation rates. The procedure consists of a single 45-min zonal ultracentrifugation step using a linear density gradient of d = 1.00 to 1.15 g/ml. Appropriate fractions of the zonal rotor effluent containing the entire VLDL spectrum were characterized by analytical ultracentrifugation, gel filtration chromatography, and complete chemical analysis. Flotation rates of VLDL subspecies from hypertriglyceridemic and normolipemic plasmas correlated directly with their Stokes radii and triglyceride content and inversely with their proportion of cholesterol, cholesteryl esters, phospholipids, and total protein. There was also an inverse correlation of flotation rate with the fraction of tetramethylurea-insoluble protein. This procedure provides a reliable methodology for a rapid isolation of VLDL subfractions and the accurate determination of their flotation rates.     

Characterisation of the small molecular weight apolipoproteins from pig plasma very low density lipoprotein.

The small molecular weight apolipoproteins of pig very low density lipoprotein were investigated following their separation by gel filtration and ion exchange chromatography. Gel filtration through Sephadex G-200 in 6 M urea, produced essentially the same elution profile to that obtained after filtration of human very low density apolipoprotein. However, separation of the pig Sephadex fraction corresponding to human C proteins on DEAE-cellulose columns revealed the presence of only one major peptide and minor quantities of several others. Some properties of three apparent homogeneous fractions and one heterogeneous DEAE fraction were investigated. Unlike human apoprotein CII apoprotein, none of the pig peptides studied activated cow's milk lipase and sialic acid was not detected in any of the three purified C peptides of pig VLDL. The amino acid compositions of the pig peptides were different to those reported for human C apoproteins. The carboxy terminal residue of the major pig C peptide was shown to be serine. The differences so far revealed between pig and human C peptides need further investigation especially since this animal is regarded as a suitable model for investigating human lipoprotein metabolism and the development of atherosclerosis.     

Isolation, characterization and comparative aspects of the major serum apolipoproteins, B-100 and AI, in the common marmoset, Callithrix jacchus

The two major apolipoproteins of marmoset serum have been isolated and characterized, and on the basis of physicochemical and immunological criteria are homologous with the human AI and B-100 proteins. Marmoset apolipoprotein AI was the principal protein of high-density lipoproteins (HDL) and was purified by gel filtration chromatography and electrophoresis in alkaline-urea polyacrylamide gel followed by electrophoretic elution. Purified marmoset apolipoprotein AI displayed an Mr of approx. 27000, was polymorphic (five forms) on isoelectric focussing, with pI values in the range 4.8-5.0, and migrated similarly to human apolipoprotein AI in alkaline-urea gels. An overall resemblance was seen in the amino acid composition of marmoset apolipoprotein AI and that of its human counterpart with the notable exception that marmoset AI contained 1 isoleucine residue/mole. An immunological reaction of partial identity between the human and monkey proteins was seen upon immunodiffusion of their HDLs against antiserum to human apolipoprotein AI. Marmoset B-100 was the predominant apoprotein of VLDL and LDL, resembling the human protein in its elution profile on gel filtration chromatography in anionic detergent, and in its high apparent Mr (approx. 520000). The marmoset and human B-100 proteins were alike in amino acid composition and carbohydrate content. Moreover, their immunological behaviour with an antiserum to marmoset apolipoprotein B showed them to share certain antigenic determinant(s). We conclude that the physicochemical properties of the principle apolipoproteins of Callithrix jacchus, a New World primate, markedly resemble those of the human AI and B-100 proteins, suggesting therefore that they may function similarly in lipid transport and metabolism. Counterparts to human apolipoproteins AII, E, CII and CIII have also been tentatively identified.     

Isolation of corticotropin-beta-lipotropin common precursor from ovine pituitary glands

Ovine corticotropin-beta-lipotropin common precursor was purified to homogeneity from commercial frozen ovine pituitary glands. A crude preparation was obtained following a procedure published elsewhere (Lee, T.H. and Lee, M.S. (1977) Biochemistry 16, 2824-2829) and was purified by gel filtration on Sephadex G-200 in the presence of 0.5% SDS and 0.1% 2-mercaptoethanol, and under an atmosphere of nitrogen. The gel filtration was repeated once. The partially purified preparation obtained from the second Sephadex G-200 gel filtration was further fractionated by preparative SDS-acrylamide gel electrophoresis, using immunoprecipitated and electrophoretically purified [125I]corticotropin-beta-lipotropin common precursor as a marker. The preparation was judged homogeneous by the appearance of a single protein band in analytical SDS-acrylamide gel electrophoresis, which exhibited both corticotropin and beta-lipotropin immunoreactivities, and a single symmetrical peak in high-pressure liquid chromatography on a reverse phase C18 column. The isolated ovine corticotropin-beta-lipotropin common precursor possessed specific activities of 116 micrograms of immunoreactive corticotropin and 210 micrograms of immunoreactive beta-lipotropin per mg of protein, equivalent to 89 and 62% of theoretical values, respectively. The amino acid composition of the homogeneous preparation was determined.     

Synthesis by an improved solid-phase method of a highly acidic peptide from nucleolar nonhistone protein C23

The total synthesis of a 42-amino acid residue peptide corresponding to the proposed sequence of a highly acidic fragment of nucleolar nonhistone protein C23 was accomplished by an improved, mild solid-phase method, employing a p-alkoxybenzyl alcohol polystyrene resin. The symmetrical anhydride and active ester coupling were used exclusively. Coupling monitoring and amino acid analyses were carried out during the stepwise synthesis. The synthetic product was purified by gel filtration and ion-exchange chromatography, and found to be homogeneous by seven additional criteria. Phosphorylation of serine residues was attempted enzymatically, and the phosphopeptides obtained had electrophoretic mobilities comparable to that of the natural product.     

Isolation of corticotropin-β-lipotropin common precursor from ovine pituitary glands

Ovine corticotropin-β-lipotropin common precursor was purified to homogeneity from commercial frozen ovine pituitary glands. A crude preparation was obtained following a procedure published elsewhere (Lee, T.H. and Lee, M.S. (1977) Biochemistry 16, 2824–2829) and was purified by gel filtration on Sephadex G-200 in the presence of 0.5% SDS and 0.1% 2-mercaptoethanol, and under an atmosphere of nitrogen. The gel filtration was repeated once. The partially purified preparation obtained from the second Sephadex G-200 gel filtration was further fractionated by preparative SDS-acrylamide gel eletrophoresis, using immunoprecipitated and electrophoretically purified [¹²⁵I]corticotropin-β-lipotropin common precursor as a marker. The preparation was judged homogenous by the appearance of a single protein band in analytical SDS-acrylamide gel electrophoresis, which exhibited both corticotropin and β-lipotropin immunoreactivities, and a single symmetrical peak in high-pressure liquid chromatography on a reverse phase C18 column. The isolated ovine corticotropin-β-lipotropin common precursor possessed specific activities of 116 μg of immunoreactive corticotropin and 210 μg of immunoreactive β-lipotropin per mg of protein, equivalent to 89 and 62% of theoretical values, respectively. The amino acid composition of the homogeneous preparation was determined.     

Heparan sulfate proteoglycans of human lung fibroblasts. Structural heterogeneity of the core proteins of the hydrophobic cell-associated forms

Heparan sulfate proteoglycans (HSPG) were solubilized from human lung fibroblast monolayers with detergent. Presumptive membrane-associated forms displaying hydrophobic properties were purified by gel filtration on Sepharose CL-4B, by ion-exchange chromatography on Mono Q and by incorporation in lipid vesicles. The HSPG preparations were 125I-iodinated and treated with heparitinase before sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Five radiolabeled proteins with apparent molecular weights of 125,000, 90,000, 64,000, 48,000, and 35,000 were visualized by autoradiography. A sixth protein, identified in nonreduced 125I-HSPG preparations, appeared as a non-HS chain-bearing Mr 35,000 peptide which was disulfide-linked to an HS chain-bearing peptide of similar size. This multiplicity of core proteins did not seem to result from proteolysis during the heparitinase treatment itself, since some of the core proteins migrated independently during gel filtration before heparitinase digestion. Moreover, heparitinase digestion of 125I-HSPG purified by affinity chromatography on an immobilized monoclonal antibody yielded only the Mr 64,000 protein. Alternative depolymerizations of the HS chains by heparinase or HNO2 also yielded multiple protein bands. These results imply that heterogeneity of the core protein moiety may be a genuine property of the hydrophobic HSPG of human lung fibroblasts. The occurrence of multiple integral membrane HSPG forms may be relevant for the multiple functions that have been ascribed to cell-surface HSPG.     

Solid phase peptide synthesis of 15N-gramicidins A, B, and C and high performance liquid chromatographic purification

Four single-site 15N-labeled molecules of gramicidin have been synthesized using the 9-fluorenylmethoxycarbonyl method of solid phase peptide synthesis. Formylvaline was coupled as the N-terminal amino acid, and the peptide was cleaved from the resin with ethanolamine. Each synthesized gramicidin was purified in one step by semipreparative reverse phase high performance liquid chromatography and obtained in overall yields as high as 86%. The peptide was characterized by comparison with natural gramicidin using amino acid analysis, u.v. spectroscopy, and analytical high performance liquid chromatography.     

Measurement of apolipoprotein A-I in rat high density lipoprotein and in rat plasma by radioimmunoassay.

A double antibody radioimmunoassay (RIA) for rat apolipoprotein A-I is reported. The ApoA-I isolated from delipidated HDL by gel filtration yielded a single band on polyacrylamide gel electrophoresis in sodium dodecyl sulfate (SDS), and its amino acid composition resembled that reported by others. ApoA-I was iodinated by lactoperoxidase and the resulting 125I-apoA-I was purified by gel filtration. Up to 93% of 125I-apoA-I was precipitable by antibody and greater than 99% of bound 125I-apoA-I was displaced by "cold" apoA-I. Other rat lopoproteins and apolipoproteins did not react in this system. Human plasma were also not reactive, nor were dog, goat, and sheep plasmas.     

Isolation of a tripeptide showing weak acetylthiocholine hydrolysing activity from a soluble form of monkey basal ganglia acetylcholinesterase by limited trypsin digestion

Acetylcholinesterase was purified from the soluble supernatant of monkey (Macaca radiata) brain basal ganglia by a three-step affinity purification procedure. The purified enzyme showed two major protein bands corresponding to molecular weights of approximately 65 kDa and approximately 58 kDa which could be labelled by [3H]diisopropylfluorophosphate. When the purified enzyme was subjected to limited trypsin digestion followed by gel filtration on Sephadex G-75 or Sephadex G-25 column, a peptide fragment of molecular weight approximately 300 Da having a weak acetylthiocholine hydrolysing activity was isolated. The amino acid sequence analysis of this peptide showed a sequence of Gly-Pro-Ser. When the [3H]DFP labelled enzyme was subjected to limited trypsin digestion and Sephadex G-75 column chromatography, a labelled peptide corresponding to approximately 430 Da was isolated. The kinetics, inhibition characteristics and binding characteristics to lectins of this peptide were compared with the parent enzyme. A synthetic peptide of sequence Gly-Pro-Ser was also found to exhibit acetylthiocholine hydrolysing activity. The kinetics and inhibition characteristics of the synthetic peptide were similar to those of the peptide derived from the purified acetylcholinesterase, except that the synthetic peptide was more specific towards acetylthiocholine than butyrylthiocholine. The specific activity (units/mg) of the synthetic peptide was about 123700 times less than that of the purified AChE.     

Purification and partial characterization of lactacin F, a bacteriocin produced by Lactobacillus acidophilus 11088.

Lactacin F, a bacteriocin produced by Lactobacillus acidophilus 11088 (NCK88), was purified and characterized. Lactacin F is heat stable, proteinaceous, and inhibitory to other lactobacilli as well as Enterococcus faecalis. The bacteriocin was isolated as a floating pellet from culture supernatants brought to 35 to 40% saturation with ammonium sulfate. Native lactacin F was sized at approximately 180 kDa by gel filtration. Column fractions having lactacin F activity were examined by electron microscopy and contained micelle-like globular particles. Purification by ammonium sulfate precipitation, gel filtration, and high-performance liquid chromatography resulted in a 474-fold increase in specific activity of lactacin F. The purified bacteriocin was identified as a 2.5-kDa peptide by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The lactacin F peptide retained activity after extraction from SDS-PAGE gel slices, confirming the identity of the 2.5-kDa peptide. Variants of NCK88 that failed to exhibit lactacin F activity did not produce the 2.5-kDa band. Sequence analysis of purified lactacin F identified 25 N-terminal amino acids containing an arginine residue at the N terminus. Composition analysis indicates that lactacin F may contain as many as 56 amino acid residues.     

Purification and partial characterization of lactacin F, a bacteriocin produced by Lactobacillus acidophilus 11088

Lactacin F, a bacteriocin produced by Lactobacillus acidophilus 11088 (NCK88), was purified and characterized. Lactacin F is heat stable, proteinaceous, and inhibitory to other lactobacilli as well as Enterococcus faecalis. The bacteriocin was isolated as a floating pellet from culture supernatants brought to 35 to 40% saturation with ammonium sulfate. Native lactacin F was sized at approximately 180 kDa by gel filtration. Column fractions having lactacin F activity were examined by electron microscopy and contained micelle-like globular particles. Purification by ammonium sulfate precipitation, gel filtration, and high-performance liquid chromatography resulted in a 474-fold increase in specific activity of lactacin F. The purified bacteriocin was identified as a 2.5-kDa peptide by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The lactacin F peptide retained activity after extraction from SDS-PAGE gel slices, confirming the identity of the 2.5-kDa peptide. Variants of NCK88 that failed to exhibit lactacin F activity did not produce the 2.5-kDa band. Sequence analysis of purified lactacin F identified 25 N-terminal amino acids containing an arginine residue at the N terminus. Composition analysis indicates that lactacin F may contain as many as 56 amino acid residues.     

The chemistry of the collagen cross-links. Purification and characterization of cross-linked polymeric peptide material from mature collagen containing unknown amino acids.

A polymeric form of the alpha 1-chain C-terminal peptide alpha 1 CB6 (poly-alpha 1 CB6) was purified from CNBr digests of insoluble bovine tendon type-I-collagen by gel filtration and ion-exchage chromatography. The purified material had a molecular weight of 1.5 x 10(6)-5 x 10(6) on gel filtration and an amino acid content virtually identical with that of monomeric peptide alpha 1 CB6. The material could be adsorbed on affinity gels containing immobilized anti-(alpha 1 CB6-peptide non-helical region) antibodies and was an inhibitor of haemagglutination by the same antibodies of alpha 1 CB6-peptide-coated sheep erythrocytes. Periodate treatment of the material had no effect. Alkali hydrolysates were shown to contain two unknown amino acids, which were purified by gel filtration and ion-exchange chromatography in volatile buffers and are believed to be components of the mature cross-link of collagen.     

Cell-free synthesis of cod preproinsulin

Poly(A)-containing ribonucleic acid from cod islet greatly stimulated the incorporation of radioactive amino acids into proteins when assayed in a wheat germ translation system. The translation products were examined by specific immunoprecipitation with guinea pig anti cod insulin antibodies and by extraction with acid--ethanol. These measurements revealed at least a fivefold increase in incorporation of labelled amino acid over the nonprogrammed system. Sodium dodecyl sulfate disc gel electrophoresis and gel filtration chromatography showed a product of molecular weight 12 500, a size considerably larger than cod proinsulin (9000). It is concluded that cod proinsulin is synthesized via a larger precursor, preproinsulin.     

Effects of oleic acid on the biosynthesis of lipoprotein apoproteins and distribution into the very-low-density lipoprotein by the isolated perfused rat liver.

The effects of oleic acid on the biosynthesis and secretion of VLDL (very-low-density-lipoprotein) apoproteins and lipids were investigated in isolated perfused rat liver. Protein synthesis was measured by the incorporation of L-[4,5-3H]leucine into the VLDL apoproteins (d less than 1.006) and into apolipoproteins of the whole perfusate (d less than 1.21). Oleate did not affect incorporation of [3H]leucine into total-perfusate or hepatic protein. The infusion of oleate, however, increased the mass and radioactivity of the VLDL apoprotein in proportion to the concentration of oleate infused. Uptake of oleate was similar with livers from fed or fasted animals. Fasting itself (24 h) decreased the net secretion and incorporation of [3H]leucine into total VLDL apoprotein and decreased the output of VLDL protein by the liver. A linear relationship existed between the output of VLDL triacylglycerol (mumol/h per g of liver) and secretion and/or synthesis of VLDL protein. Net output of VLDL cholesterol and phospholipid also increased linearly with VLDL-triacylglycerol output. Oleate stimulated incorporation of [3H]leucine into VLDL apo (apolipoprotein) E and apo C by livers from fed animals, and into VLDL apo Bh, B1, E and C by livers from fasted rats. The incorporation of [3H]leucine into individual apolipoproteins of the total perfusate lipoprotein (d less than 1.210 ultracentrifugal fraction) was not changed significantly by oleate during perfusion of livers from fed rats, suggesting that the synthesis de novo of each apolipoprotein was not stimulated by oleate. This is in contrast with that observed with livers from fasted rats, in which the synthesis of the total-perfusate lipoprotein (d less than 1.210 fraction) apo B, E and C was apparently stimulated by oleate. The observations with livers from fed rats suggest redistribution of radioactive apolipoproteins to the VLDL during or after the process of secretion, rather than an increase of apoprotein synthesis de novo. It appears, however, that the biosynthesis of apo B1, Bh, E and C was stimulated by oleic acid in livers from fasted rats. Since the incorporations of [3H]leucine into the VLDL and total-perfusate apolipoproteins were increased in fasted-rat liver when the fatty acid was infused, part of the apparent stimulated synthesis of the VLDL apoprotein may be in response to the increased formation and secretion of VLDL lipid.     

Iodination of proteins,glycoproteins, and peptides using a solid-phase oxidizing agent, 1,3,4,6-tetrachloro-3α,6α-diphenyl glycoluril (Iodogen)

A new, commercially available oxidizing agent, 1,3,4,6-tetrachloro-3α,6α-diphenyl glycoluril (Iodogen) was compared with chloramine-T and solid-phase lactoperoxidase in the radioiodination of proteins, glycoproteins, and peptides. A method for performing low-level iodinations is described and was used to determine maximum ¹²⁵I incorporation. Iodinated proteins were purified on analytical gel filtration columns and peptides by reverse-phase high-performance liquid chromatography. Both methods were designed to analyze the tracers for the presence of aggregate and breakdown products caused by the iodination. All tracers prepared were tested in antibody dilution and dose-response curves in their respective radioimmunoassays. Results indicate that Iodogen can be used for a wide range of proteins and peptides, can permit theoretical iodine incorporation with minimal oxidation damage, and can produce tracer stable for up to 3 months.