Affinity purification and characterization of serine hydroxymethyltransferases from rat liver

A rapid and simple method was developed for the purification of serine hydroxymethyltransferases [EC 2.1.2.1]. The procedure involved ammonium sulfate precipitation, DEAE-cellulose column chromatography and affinity chromatography on an L-adsorbent. Through this procedure the cytosolic enzyme (s-SHMT) was purified 1,650-fold, and the mitochondrial enzyme (m-SHMT) 1,730-fold, with a yield of more than 30% in both cases. Both preparations gave a single band with a Mr of 54,000 on SDS-PAGE. The native enzymes both contained 4 mol of pyridoxal phosphate/mol of enzyme, and showed a Mr value of 220,000 on gel filtration, indicating a tetrameric structure. Several other properties of the enzymes were also studied.     

Partial purification of a high density lipoprotein-binding protein from rat liver and kidney membranes

The existence of a cell receptor which recognises plasma high density lipoprotein (HDL) has been suggested from studies which demonstrate specific binding of HDL3 to cultured cells derived from various tissues in the body. This study provides evidence of a specific HDL-binding protein in crude plasma membranes prepared from rat kidney and liver. Following separation of solubilised membrane proteins on polyacrylamide gel slabs and 'Western' blotting, one major band was identified which bound HDL3, or apo AI or apo AII. The protein, which was present in both liver and kidney membranes, was partially purified by repetitive preparative SDS-polyacrylamide gel electrophoresis and although accompanied by considerable loss of binding activity, could still be detected by the ligand-blotting procedure used initially to detect its presence in cell membranes.     

Affinity chromatography of rat liver aminoacyl-tRNA synthetase complex

The affinity column lysyldiaminohexyl-Sepharose 4B has been synthesized for the purification of aminoacyl-tRNA synthetase complexes. Lysyl-tRNA synthetase (EC 6.1.1.6) bound specifically to the Sepharose-bound lysine. The purified lysyl-tRNA synthetase was associated with arginyl-tRNA synthetase (EC 6.1.1.16) and sedimented at 18S and 12S. A 24S lysyl-tRNA synthetase bound specifically to the affinity column and also found associated with arginyl-tRNA synthetase. The results favor the model of a heterotypic multienzyme complex of mammalian aminoacyl-tRNA synthetases.     

Affinity purification of insulin-degrading enzyme and its endogenous inhibitor from rat liver.

A metallothiol protease called insulin-degrading enzyme (IDE) seems to be implicated in insulin metabolism to terminate the response of cells to hormone, as well as in other biological functions, including muscle differentiation, regulation of growth factor levels, and antigen processing. In order to obtain highly pure and biologically active IDE, we have developed an immunoaffinity method using a monoclonal antibody to this enzyme (9B12). When the cytosolic fraction of rat liver was first applied to a 9B12-coupled Affi-Gel 10 column, more than 97% of the insulin-degrading activity was absorbed. Among various kinds of buffers successfully eluting the enzyme, only the buffer with a high pH (pH 11) could retain the full biological activity of this enzyme. IDE was further purified via two steps of chromatography using Mono Q anion exchange and Superose 12 molecular sieve columns. The final preparation showed a single band at 110 kDa on reduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In the eluate from the immunoaffinity column, the inhibitory activity associated with the enzyme was also observed. To better recover this endogenous inhibitor, heat-treated cytosolic fraction was fractionated by ammonium sulfate precipitation and applied to the immunoaffinity column on which IDE had been adsorbed. Then, IDE and its inhibitor could be co-eluted with pH 11 as a complex form. After heat treatment of this fraction, the inhibitor was further purified using the same series of chromatography as IDE to more than 20,000-fold; it showed a 14 kDa band on SDS-PAGE. It inhibited both the insulin degradation by IDE in a competitive manner and the cross-linking of 125I-insulin to IDE. Highly purified IDE and the endogenous inhibitor will be useful tools for better understanding the various biological functions of this enzyme.     

Affinity purification and some properties of nucleoside diphosphatase from rat liver cytosol.

Nucleosidediphosphatase (nucleosidediphosphate phosphohydrolase, EC 3.6.1.6) of rat liver cytosol was purified up to 336--fold by the procedure including affinity chromatographies of concanavalin A- and alanine-Sepharose. The final purified enzyme showed a single protein band upon polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Its native form was found to be a tetramer with molecular weight of 120 000 which consists of subunit with molecular weight of 30 000. The enzyme was found to be a glycoprotein on the basis of its chromatographic behaviour with concanavalin A-Sepharose and positive staining with periodate-Schiff reaction in polyacrylamide gels. Furthermore, the two molecular forms with isoelectric points of 4.7 and 5.0 were demonstrated by electrofocusing, though they did not show any significant difference with respect to their catalytic properties.     

Chromatin-nuclear envelope complex from rat liver: isolation and purification

We describe a method for the isolation of a fraction of nuclear envelope (NE) from rat liver. The method includes mild treatment of pure nuclei with either endonuclease of DNase I under low ionic strength conditions in the presence of magnesium, which allows the nucleomeric organization of the chromatin (Ch) to be preserved. The NEs were purified by centrifugation in sucrose gradients followed by floatation in sucrose. No more than 3% of the Ch present in the purified Ch-NE complexes was due to the non specific adsorption of Ch to the NE. The main components of the complex (Ch and NE) retained their in situ ultrastructure. The complex consisted of 9--10% DNA, 3--4% RNA, about 63% protein and about 24% phospholipids.     

The purification and characterization of mannosidase IA from rat liver Golgi membranes

Rat liver Golgi membranes contain two alpha 1,2-specific mannosidases (IA and IB) (Tulsiani, D. R. P., Hubbard, S. C., Robbins, P. W., and Touster, O. (1982) J. Biol. Chem. 257, 3660-3668). Mannosidase IA has now been purified to apparent homogeneity by detergent extraction and (NH4)2SO4 precipitation, followed by Sephacryl S-300, ion-exchange, and hydroxylapatite chromatography. The enzyme was homogeneous by nondenaturing polyacrylamide gel electrophoresis with different gel concentrations, and Ferguson plot analysis indicated an Mr of 230,000 for the native enzyme. Although electrophoresis under denaturing conditions generally gave a subunit Mr of 57,000, electrophoresis of less than 1 microgram of protein yielded a faint doublet of Mr 57,000 and 58,000. Thus, the enzyme appears to be a tetramer with four very similar subunits. The enzyme bound to concanavalin A-Sepharose 4B only when it was kept in contact with the lectin for 16 h. Endoglycosidase H treatment resulted in loss of its binding to the lectin, without leading to a detectable change in the size of the enzyme subunit. On electrophoretic gels, the enzyme gave a faint positive stain with periodic acid-Schiff's base. The enzyme contained about 0.9% hexose by direct analysis. It did not bind to affinity resins specific for neuraminic acid, galactose, or N-acetylglucosamine. All these studies suggest that the enzyme is a glycoprotein containing only one or two clusters of high mannose oligosaccharide. Mannosidase IA is active toward oligosaccharides containing alpha 1,2-linked mannosyl residues. [3H]Man9GlcNAc, [3H] Man8GlcNAc, [3H]Man7GlcNAc, and [3H]Man6GlcNAc are good substrates. Man9GlcNAc, the best substrate, yields Man8, Man7, and Man6 derivatives with structures suggesting that the sequence of release of mannose residues is rather specific. Immunoprecipitation studies using polyclonal antibody (IgG) prepared against homogeneous mannosidase IA cross-reacted with mannosidase IB, a result suggesting that these two enzymes share antigenic determinants. However, no cross-reactivity was observed with rat liver cytosolic and lysosomal alpha-D-mannosidases or with Golgi mannosidase II.     

Partial purification and characterization of a serine endopeptidase from rat liver plasma membranes

A serine endopeptidase was partially purified from rat liver plasma membranes by using a four-step procedure: solubilization with N-lauroylsarcosine; Ultrogel AcA-34 chromatography; CM Affi-Gel blue chromatography; agarose-soybean trypsin inhibitor chromatography. This enzyme was found to hydrolyze casein and various chromogenic peptide substrates; highest activity occurred with H-D-Val-Leu-Arg-p-nitroanilide, reported to be a specific substrate for human glandular kallikreins. The enzyme was heat-sensitive, showed a pH optimum between 8.0 and 9.0 and was inhibited by D-Phe-L-Phe-L-Arg-CH2Cl, aprotinin, diisopropyl fluorophosphate (DFP), soybean trypsin inhibitor, phenylmethylsulphonyl fluoride, leupeptin, antipain and dithiothreitol. This liver plasma membrane proteinase has an apparent molecular weight of about 30 000 as determined by Ultrogel AcA-34 chromatography and by autoradiography of [3H]DFP-labelled protein electrophoresis.     

Affinity purification of alkylglycerol monooxygenase from rat liver microsomes by chimyl alcohol-Sepharose 4B column chromatography

Alkylglycerol monooxygenase of rat liver microsomes was purified approximately to 97-fold with a 30% yield by procedures including affinity chromatography on chimyl alcohol-Sepharose 4B. Chimyl alcohol (1-O-hexadecylglycerol) was converted to the p-aminobenzylidene derivative and then coupled to 6-carboxyhexyl-Sepharose. The final enzyme preparation was in nearly a homogeneous state, judging from the results of sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis, and it migrated to a position corresponding to an apparent molecular weight of 45,000. The results revealed that the native form of the enzyme (estimated to have a molecular weight of 400,000 as judged by Sepharose 6B column chromatography in a previous report, Ishibashi, T., and Y. Imai. 1983. Eur. J. Biochem. 132: 23-27) will polymerize to large aggregates.     

Affinity ligands for industrial protein purification

Significant efforts are put into the design of large-scale purification processes of proteins due to great demands regarding cost efficiency and safety. In order to design an effective purification scheme the unit operations need to be reduced to a minimum. In this review we are discussing proteinaceous ligands as well as small synthetic mimics for use in affinity chromatography for large-scale applications. Different advantages as well as drawbacks of the two approaches are outlined.     

Characterization and partial purification of protein fatty acyltransferase activity from rat liver

The acylation of proteins through the addition of palmitate to cysteine residues is a common posttranslational modification for a variety of proteins, but the enzymology of this reversible modification has resisted elucidation. We developed a strategy to purify protein fatty acyltransferase (PAT) activity from rat livers that took advantage of recent knowledge on the cellular location and inhibition of PAT activity. We determined that three different thiolases have PAT activity in the presence of imidazole and therefore started the purification with a plasma membrane fraction to minimize the contamination with these enzymes. After detergent extraction of the plasma membrane fraction, the PAT activity was enriched about 90-fold by sequential chromatography including affinity chromatography to a cerulenin-based inhibitor of palmitoylation. The partially purified PAT activity (1) was lost with treatments to degrade or denature proteins, (2) could acylate tubulin, Galpha(i) and RGS16 and (3) showed a preference for palmitate and to a lesser degree other long-chain fatty acids. This purification procedure is a significant advance over previous efforts at PAT purification and a starting point for a proteomic approach for identification of mammalian PAT.     

Affinity chromatographic purification and properties of flavokinase (ATP:riboflavin 5'-phosphotransferase) from rat liver

Flavokinase (ATP:riboflavin 5'-phosphotransferase, EC 2.7.1.26) has been purified to apparent homogeneity from rat liver by affinity chromatography using flavinyl agarose beads (agarose-OCH2CONH(CH2)2NHCO(CH2)/N10-7,8-dimethylisoalloxazine). The specific activity of the pure enzyme is 9,900 units (nmol of FMN formed/h at 37 degrees C)/mg of protein, and reflects a one-step, 7000-fold purification. Flavokinase thus obtained, unlike previous preparations from mammalian sources, is free from contaminating phosphatase and FAD synthase. The purified enzyme rapidly loses activity upon storage but is stabilized by riboflavin and thiol-protecting reagents. The apparent molecular weight, estimated by gel filtration on Sephadex G-100 and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, is 28,000 +/- 1,000. Flavokinase phosphorylates and/or is inhibited by a large number of riboflavin analogs; however, the physiologically important 8 alpha-(amino acid)riboflavins are poorly accommodated. The strongly preferred phosphate donors are ATP and dATP. Both Zn2+ and Mg2+, as well as several other divalent cations, activate flavokinase, but Zn2+ yields greatest activity (1.8 times that with Mg2+). The pH optimum for activity with either Zn2+ or Mg2+ is approximately 9.3; at pH 7.0, the activity is 40% of that at the pH optimum.     

Partial purification of diphosphatidylglycerol synthetase from liver mitochondrial membranes

The enzyme responsible for the conversion of phosphatidylglycerol to diphosphatidylglycerol (cardiolipin) in the presence of cytidine diphosphate diacylglycerol is firmly associated with mitochondrial membranes and is not extracted with hypotonic or hypertonic media or with nonionic detergents. Some solubilization was obtained with bile salt solutions, but the zwitter-ionic detergent. Miranol H2M, was most effective in extracting the enzyme. The Miranol extracts were fractionated by column chromatography on Bio-Gel A-1.5 m. The solubilized enzyme is considerably more active in converting unsaturated than saturated phosphatidyl-glycerols, but shows little preference for the cytidine diphosphate diacylglycerols with different fatty acyl substituents. There is an absolute dependence upon divalent cations with the order of effectiveness: Co2+ much greater than Mn2+ greater than Mg2+. In the presence of optimal levels of Co2+ other divalent cations are inhibitory with the order of inhibition: Cd2+ greater than Zn2+ greater than Ca2+ greater than Ba2+ greater than Cu2+ greater than Hg2+ greater than Ni2+. The solubilized enzyme exhibited no requirement for added phospholipids and several phospholipids inhibited the reaction in the order: diphosphatidylglycerol greater than phosphatidylethanolamine greater than phosphatidylserine greater than phosphatidylinositol.     

Solubilization of the vasopressin receptor from rat liver plasma membranes. Evidence for a receptor X GTP-binding protein complex

The GTPase activity of plasma membranes isolated from rat livers was stimulated 20% over basal by vasopressin. A concentration dependency curve showed that maximal stimulation was obtained with 10(-8) M vasopressin. The vasopressin-stimulated GTPase activity was not inhibited in plasma membranes that had been ADP-ribosylated with either cholera toxin or pertussis toxin. Identical results were obtained from plasma membranes that had been solubilized with 1% digitonin. When membranes that had been solubilized after preincubation with [3H]vasopressin were subjected to sucrose gradient centrifugation, the majority of protein-bound [3H]vasopressin migrated as a single band with a sedimentation constant of 16.8 S. Moreover, there was a GTPase activity that migrated with the bound [3H]vasopressin. This peak of bound [3H]vasopressin was decreased by 90% when the sucrose gradient centrifugation was run in the presence of 10 microM guanosine 5'-O-(thiotriphosphate). When the 16.8 S peak of bound [3H]vasopressin was further purified over a wheat germ lectin-Sepharose column, a GTPase activity co-eluted from the column with the protein-bound [3H]vasopressin. Direct evidence that a GTP-binding protein was present in the 16.8 S peak was obtained by the immunodetection of a 35-kDa beta subunit of a GTP-binding protein. These results support the conclusion that liver plasma membranes contain a GTP-binding protein that can complex with the vasopressin receptor.     

Steroid-affinity purification of the rat liver glucocorticoid hormone receptor complex

The molybdate-stabilized GHRC was isolated from rat liver cytosol with a 9000-fold purification and 46% yield. The major purification step was achieved using an affinity matrix consisting of an agarose support coupled to a dexamethasone ligand via an aliphatic spacer arm. Spacer arms containing disulfide bridges were found to be unsuitable due to their instability in cytosol. To reduce the non-specific binding properties of the affinity matrix, underivatized amino groups were acetylated, since the receptor was found to bind avidly to such groups thus evading elution by the ligand. Sodium molybdate present during biospecific elution from the gel stabilized the steroid-binding activity of the receptor. The use of denaturing and sulfhydryl modifying reagents (NaSCN, DMSO, Mersalyl) during elution led to partial or complete irreversible loss of steroid-binding activity of the unoccupied receptor. Efficient biospecific elution occurred at competing concentration of high affinity steroid in the presence of sodium molybdate. The ligand specific eluate was further purified by DEAE-Sephacel chromatography resulting in additional purification of 3.2-fold. The GHRC eluted from the DEAE-Sephacel column at a salt concentration characteristic of the untransformed GHRC. Molybdate was removed from the purified untransformed GHRC in the ligand eluate by DEAE-Sephacel chromatography in the absence of molybdate, for subsequent heat transformation.     

High-yield purification of glucokinase from rat liver

A rapid and reliable method for the purification of rat liver glucokinase was developed. The procedure consists of DEAE-cellulose ion-exchange chromatography, Phenyl-Sepharose hydrophobic interaction chromatography, DEAE-Affi Gel Blue dye-ligand chromatography, and duplicate steps of glucosamine-Sepharose affinity chromatography. Glucokinase was purified to a specific activity of 290 units/mg protein in a yield of 55% in 6 days. The final enzyme preparations were completely homogeneous in most experiments as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The estimated molecular weight (51,000) and sigmoidal saturation function for glucose of purified glucokinase were in good agreement with published data.     

Acid phosphatase in rat liver lysosomal membranes: purification and characterization

Acid phosphatase associated with rat liver lysosomal membranes (M-APase) was purified about 4,200-fold over the homogenate with 10% recovery to apparent homogeneity, as determined from the pattern on polyacrylamide gel electrophoresis in the presence of SDS. The purification procedure included; preparation of lysosomal membranes, solubilization of the membranes with 1% Triton X-100, immunoaffinity chromatography, and gel filtration with FPLC equipped with a Sephacryl S-300HR column. The molecular weight, estimated by gel filtration through TSK SW 3000G, was approximately 320K and SDS gel electrophoresis showed that the enzyme is composed of four identical subunits with an apparent molecular weight of 67K. The enzyme contains about 24.3% carbohydrate consisting of mannose, galactose, fucose, N-acetylglucosamine, N-acetylgalactosamine, and N-acetylneuraminic acid in a molar ratio of 38:20:5:36:4:11, respectively. In addition, three soluble forms of acid phosphatase (C-APase I, II, and III) in lysosomal contents were separated from rat liver lysosomal contents with DEAE-Sephacel. These three enzymes were also purified using immunoaffinity chromatography followed by gel filtration. C-APase I, II, III, and M-APase have isoelectric points of 7.7-8.2, 6.6-7.0, 5.7-6.7, and 3.4-3.8, respectively. All four APases are sensitive to endo-beta-N-acetylglucosaminidase H. However, only C-APase III and M-APase are digestible with neuraminidase. Susceptibility of M-APase to neuraminidase in intact tritosomes was examined to study the topography of M-APase in tritosomal membranes. Neuraminidase susceptibility of M-APase was not observed in the intact tritosomes until the tritosomes had been disrupted by osmotic shock.(ABSTRACT TRUNCATED AT 250 WORDS)