Purification and characterization of osteopontin from human milk

Osteopontin (OPN) is expressed in many organs and tissues and has different biological properties related to different molecular forms in respect to size and posttranslational modifications. However, a purification procedure for authentic intact OPN as well as fragments of OPN from an accessible biological source is missing. A four-step procedure was used to purify OPN from human milk, based on its crystal growth inhibitory activity, including anion exchange chromatography, the elimination of casein, hydroxyapatite chromatography, and negative affinity chromatography. Purified OPN was further separated into its different molecular forms by means of a two-step procedure, involving size exclusion chromatography and reverse phase chromatography. A rabbit polyclonal antibody was raised to purified intact OPN and high M(r) OPN components; the immunoreactivity of both forms was almost equal when investigated by enzyme immunoassay (EIA). The procedures facilitate the purification of intact OPN and OPN fragments for purposes of standardization, preparation of monospecific antibodies, and functional studies.     

Purification of rabbit tumor necrosis factor

Rabbit tumor necrosis factor (TNF) was purified and shown by SDS-PAGE to be a single protein of 18 kDa. TNF in 355 ml rabbit serum was precipitated with ammonium sulfate, and purified by repeated DEAE-Sephadex and Sephacryl S-200 chromatographies, and the final fractionation on Blue-Sepharose 6B. By this procedure its yield was 22% and its specific activity was 2.4 × 10⁷ U/mg protein. The sequence of the N-terminal 20 amino acids was determined.     

Differences in C-terminal amino acid sequences between erythrocyte and liver cytochrome b5 isolated from pig and human. Evidence for two tissue-specific forms of cytochrome b5

Two forms of cytochrome b5, a soluble erythrocyte form and a membrane-bound liver form, were purified from pig and human, and structural differences between them were analyzed. Porcine and human erythrocyte cytochrome b5 consisted of 97 amino acid residues and contained the same catalytic domain structure (residues 1-96) as that of the corresponding liver cytochrome b5, but had one amino acid replacement at the C-terminus (residue 97). These results suggest that erythrocyte cytochrome b5 is not derived from the liver protein by proteolysis but a translational product from another distinct mRNA of cytochrome b5.     

The erythrocyte membrane in essential hypertension characterization of the temperature dependence of lithium efflux

Erythrocytes of most patients with essential hypertension are distinguished by a typical pattern of temperature-dependence of Li efflux. In the present study we have attempted to characterize this unique temperature response. Measurements of Li efflux into Na medium and Li_i-Na_o countertransport were conducted simultaneously at finely spaced temperature intervals with increments of 1 to 2°C in the range of 10–40°C. The Arrhenius plots for the efflux in Na medium and for Li_i-Na_o countertransport in erythrocytes of both normotensives and hypertensives were biphasic with slopes representing apparent energies of activation of about 28 and 8 kcal/mol below and above the ‘break’, respectively. However, the ‘break’ in the Arrhenius plot appeared at distinctly different temperatures: 30°C for normotensives and 20°C for hypertensives. The Li efflux was resolved into N-ethylmaleimide-sensitive and -insensitive components. The sensitive component exhibited a typical biphasic temperature response, with the characteristic ‘break’: at 30°C for normotensives and at 20°C for hypertensives. In contrast, the N-ethylmaleimide-insensitive component was alike in normotensives and hypertensives. It is concluded that: (a) the unique temperature dependence of Li efflux in erythrocytes of hypertensives results from a localized modification in the membrane; (b) the N-ethylmaleimide-sensitive component represents a protein moiety which distinguishes between the erythrocyte membrane of normotensives and hypertensives; (c) the expression of the temperature dependence as judged by the sharp transition in slope (within 1 to 2°C), apparently reflects the cooperative involvement of membrane lipids, associated with the Li efflux system.     

Purification and partial characterization of A D-like fragment from human fibrinogen,produced by human leukocyte elastase

Digestion of human fibrinogen with human leukocyte elastase in the presence of Ca²⁺ yields a D-like fragment of M_r 93 000. This fragment was purified by gel filtration on Sephacryl S-200 followed by chromatofocusing. The purified fragment was partially characterized and compared with a fragment termed D-cate, which is produced by plasmin digestion of fibrinogen in the presence of Ca²⁺. The molecular weights of the constituent chains of the D-like fragment and D-cate were similar. The D-like fragment precipitated with antisera directed against D-cate, but not with antisera against fragment E. The name D-elastase for the fragment is suggested. Differences between the D-elastase and D-cate fragments were found in amino-terminal amino acids, in isoelectric point and in the expression of D antigenic determinants. Two major functional differences were demonstrated: fragment D-elastase had a much stronger anticlotting potency than D-cate and the binding of Ca²⁺ by D-elastase and D-cate differed qualitatively and quantitatively. Since it has been suggested that the calcium-binding and anticlotting properties of D-cate are related to a carboxyl-terminal 13 000 stretch of the γ-chain, the present findings for D-elastase indicate that the differences in these properties between D-cate and D-elastase are due to differences in this area of the molecule.     

Purification and characterization of two forms of a low-affinity Ca2+-ATPase from erythrocyte membranes

A low-affinity Ca²⁺-ATPase from erythrocyte membranes has been purified by agarose suspension electrophoresis and polyacrylamide gel electrophoresis in the absence of detergents. For maximal activity a calcium concentration above 10 mM is required. The activity is independent of magnesium. The $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ value for ATP is about 60 μM. The enzyme appears in two forms (A and B) with similar amino acid composition. The specific activity of A is higher than that of B. Gel electrophoresis in SDS of A gives a pattern consisting of two bands. B gives the same pattern; the only difference between the patterns is the ratio of the amounts of protein in the bands. The apparent molecular weight of the proteins in the two SDS bands has been estimated at 23 000 and 21 000, respectively. The results obtained can be explained by assuming that the two proteins corresponding to the two bands obtained in SDS electrophoresis have a similar structure and can associate to complexes A and B. We have also shown that electrophoretic and chromatographic supporting media can induce aggregation of (membrane) proteins. Artificial complexes can thus be formed and cause misinterpretation of the data obtained. This may be the reason why some authors have speculated that Ca²⁺-ATPase is active only in complex with other proteins such as spectrin and actin.     

Molecular cloning, expression, and characterization of dnaK in Streptococcus pneumoniae

DnaK is known to be highly conserved in all species and is a major immunogen in Streptococcus pneumoniae. To elucidate the role of dnaK in S. pneumoniae, dnaK was cloned in Escherichia coli using a homologous dnaK probe generated by PCR. The His-tagged DnaK was overexpressed in soluble form and purified from E. coli. Alignment of the deduced DnaK amino acid sequence from nucleotide sequences of the cloned dnaK revealed high homology with DnaK analogs in E. coli (53%) and Staphylococcus aureus (73%). However, anti-pneumococcal DnaK antiserum did not crossreact with DnaK analogs in E. coli, S. aureus and human cells suggesting that pneumococcal DnaK might be a good candidate as a vaccine.     

Productive recognition of factor IX by factor XIa exosites requires disulfide linkage between heavy and light chains of factor XIa

In the intrinsic pathway of blood coagulation factor XIa (FXIa) activates factor IX (FIX) by cleaving the zymogen at Arg(145)-Ala(146) and Arg(180)-Val(181) bonds releasing an 11-kDa activation peptide. FXIa and its isolated light chain (FXIa-LC) cleave S-2366 at comparable rates, but FXIa-LC is a very poor activator of FIX, possibly because FIX undergoes allosteric modification on binding to an exosite on the heavy chain of FXIa (FXIa-HC) required for optimal cleavage rates of the two scissile bonds of FIX. However preincubation of FIX with a saturating concentration of isolated FXIa-HC did not result in any potentiation in the rate of FIX cleavage by FXIa-LC. Furthermore, if FIX binding via the heavy chain exosite of FXIa determines the affinity of the enzyme-substrate interaction, then the isolated FXIa-HC should inhibit the rate of FIX activation by depleting the substrate. However, whereas FXIa/S557A inhibited FIX activation of by FXIa, FXIa-HC did not. Therefore, we examined FIX binding to FXIa/S557A, FXIa-HC, FXIa-LC, FXIa/C362S/C482S, and FXIa/S557A/C362S/C482S. The heavy and light chains are disulfide-linked in FXIa/S557A but not in FXIa/C362S/C482S and FXIa/S557A/C362S/C482S. In an ELISA assay only FXI/S557A ligated FIX with high affinity. Partial reduction of FXIa/S557A to produce heavy and light chains resulted in decreased FIX binding, and this function was regained upon reformation of the disulfide linkage between the heavy and the light chains. We therefore conclude that substrate recognition by the FXIa exosite(s) requires disulfide-linked heavy and light chains.     

Purification and amino acid sequence of two small, acid-soluble proteins from Clostridium bifermentans spores

Clostridium bifermentans spores contain two major small, acid-soluble, proteins (SASP) termed SASP-alpha and beta. The amino acid sequences of SASP-alpha and beta are almost identical, and are very similar to those of alpha/beta-type SASP from spores of C. perfringens and various Bacillus species. However, the C. bifermentans proteins contain an extra five amino acids in the middle of their sequence. Surprisingly, no gamma-type SASP were found in C. bifermentans or C. perfringens spores, although these are the most prominent SASP in spores of Bacillus species.     

Purification, amino acid sequence and characterization of the class IIa bacteriocin weissellin A, produced by Weissella paramesenteroides DX

Weissella paramesenteroides DX has been shown to produce a 4450-Da class IIa bacteriocin, weissellin A, composed of 43 amino acids with the sequence KNYGNGVYCNKHKCSVDWATFSANIANNSVAMAGLTGGNAGN. The bacteriocin shares 68% similarity with leucocin C from Leuconostoc mesenteroides. Computational analyses predict that the bacteriocin is a hydrophobic molecule with a beta-sheet type conformation. Weissellin A exhibited various levels of activity against all gram-positive bacteria tested, but was not active against Salmonella enterica Enteritidis. The antimicrobial activity was not associated with target-cell lysis. The bacteriocin retained activity after exposure to 121 °C for 60 min or to −20 °C for 6 months, and to pH 2.0-10.0. It was not sensitive to trypsin, α-chymotrypsin, pepsin and papain, but was inactivated by proteinase K. At a dissolved oxygen concentration of 50%, weissellin A was produced with growth-associated kinetics. The properties of weissellin A make this bacteriocin a potentially suitable agent for food and feed preservation.     

Purification and characterization of carbonic anhydrase from bovine erythrocyte plasma membrane

Carbonic anhydrase (CA) was purified from bovine erythrocyte plasma membrane and characterized in this study. For this purpose, the blood taken from young animals was hemolysed, the membrane fraction was separated, and this fraction was repeatedly washed. The enzyme (CA) was removed from the membrane with buffered TritonX-100 (1%); it could be purified at a factor of 22.8 by affinity chromatography.The CA obtained from erythrocyte membrane has an esterase activity as well as hydratase activity. The Vmax and Km of the enzyme for the substrate (p-nitrophenyl acetate) are 1.948x10(-3) mM/L x dak, and 3.596 mM, respectively. The purification degree of the enzyme was controlled by SDS-PAGE (3-10), which showed two distinct bands. It was determined that the enzyme had activity within the pH range of 4.5-9.5 and that the optimal pH was 7.5. The temperature at which it showed activity was 20-60 degrees C and optimal temperature was 37 degrees C. Molecular weight of CA was found to be 29844 and 61706 Dalton by gel filtration. On the other hand, sulfanilamide and acetazolamide affected the enzyme.     

erythro-β-hydroxyaspartic acid in bovine factor IX and factor X

To localize β-hydroxyaspartic acid in factor IX and factor X the two proteins were cleaved with cyanogen bromide and trypsin, respectively. Peptides containing β-hydroxyaspartic acid were isolated and subjected to Edman degradation. The phenylthiohydantoin derivative of β-hydroxyaspartic acid was identified by HPLC in position 3 in the factor IX fragment and in position 1 in the factor X fragment. This corresponds to position 64 in factor IX and position 63 in the light chain of factor X. The assignments were confirmed by subtractive Edman degradation and with the dansyl method.     

Purification, biochemical and molecular characterization of a metalloprotease from Pseudomonas aeruginosa MN7 grown on shrimp wastes

A protease-producing bacterium was isolated and identified as Pseudomonas aeruginosa MN7. The strain was found to produce proteases when it was grown in media containing only shrimp waste powder (SWP), indicating that it can obtain its carbon, nitrogen, and salts requirements directly from shrimp waste. The use of 60 g/l SWP resulted in a high protease production. Elastase, the major protease produced by P. aeruginosa MN7, was purified from the culture supernatant to homogeneity using acetone precipitation, Sephadex G-75 gel filtration, and ultrafiltration using a 10-kDa cut-off membrane, with a 5.2-fold increase in specific activity and 38.4% recovery. The molecular weight of the purified elastase was estimated to be 34 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration. The optimum temperature and pH for protease activity were 60 degrees C and 8.0, respectively. The activity of the enzyme was totally lost in the presence of ethylene glycol tetraacetic acid, suggesting that the purified enzyme is a metalloprotease. The purified enzyme was highly stable in the presence of organic solvents, retaining 100% of its initial activity after 60 days of incubation at 30 degrees C in the presence of dimethyl sulfoxide and methanol. The lasB gene, encoding the MN7 elastase, was isolated and its DNA sequence was determined.     

Isolation and characterization of the intact gastrin precursor from a gastrinoma

Antibodies to the extreme C-terminal region of human progastrin have been used to monitor the isolation of high-M_r immunoreactive material in a gastrinoma extract. Microsequence analysis of the product revealed amino acid residues in the first 18 positions corresponding to those predicted from the cDNA sequence for preprogastrin starting at position 22; the sequence and immunochemical data together allow the identification of this material as intact progastrin. Implications for gastrin biosynthesis are discussed.     

The isolation and characterization of a new elastase inhibitor,pre-α2-elastase inhibitor,of the horse

A new and probably unique elastase inhibitor of horse serum was identified, purified to homogeneity and called pre-α₂-elastase inhibitor of the horse. Electrophoretically it migrated immediately in front of the α₂ position. Its molecular weight was 188 000 by pore limit polyacrylamide gel electrophoresis and 225 000 by Sephadex G-200 gel filtration. The inhibitor was composed of at least two non-identical polypeptide chains of M_r 68 400 and 87 600. A banding pattern of restricted heterogeneity focused between pH 4.9 and 5.2 was revealed by isoelectric focusing. Of 13 animal, microbial and plant proteinases, horse pre-α₂-elastase inhibitor inhibited only pancreatic elastase and trypsin efficiently. Chymotrypsin was inhibited only in traces. No analogy between the elastase inhibitor and the known human serum inhibitors could be found with respect to immunological and biochemical criteria.     

Isolation and partial characterization of bacteriocins produced by Lactobacillus gasseri JCM 2124

Four antibacterially active peptides (B1 to B4) were purified from the culture broth of L. gasseri JCM 2124. The B2 peptide (gassericin B2) was determined to be 4400 Da by mass spectrometry and partially sequenced. Gassericin B2 did not show any sequence similarities to other known bacteriocins. The B1 and B3 peptides shared identical sequences with two peptides of a two-component bacteriocin from Lactobacillus acidophilus. However, synergistic activity upon complementation of B1 and B3 was not observed. Based on amino acid sequencing and molecular mass, it is suggested that B1 and B4 peptides were derived from B3 (gassericin B3).     

Effects of weight loss on erythrocyte membrane composition and fluidity in overweight and moderately obese women

A previous study showed chemical and physical impairment of the erythrocyte membrane of overweight and moderately obese women. The present study investigated the effects of a low-calorie diet (800 kcal/day deficit for 8 weeks) on erythrocyte membrane properties in 70 overweight and moderately obese (body mass index, 25-33 kg/m²) normotensive, nondiabetic women. At the end of dietary intervention, 24.3% of women dropped out, 45.7% lost less than 5% of their initial weight (Group I) and only 30% of patients lost at least 5% of their initial body weight (Group II). Group I showed no significant changes in erythrocyte membrane composition and function. The erythrocyte membranes of Group II showed significant reductions in malondialdehyde, lipofuscin, cholesterol, sphingomyelin, palmitic acid and nervonic acid and an increase in di-homo-γ-linolenic acid, arachidonic acid and membrane fluidity. Moreover, Group II showed an improvement in total cholesterol, low-density lipoprotein cholesterol, glycemia and insulin resistance. These changes in erythrocyte membrane composition could reflect a virtuous cycle resulting from the reduction in insulin resistance associated with increased membrane fluidity that, in turn, results in a sequence of metabolic events that concur to further improve membrane fluidity.     

Purification and characterization of the major sialoglycoproteins of the rat erythrocyte membrane

The major sialoglycoproteins of the rat erythrocyte membrane were purified by hot phenol partitioning followed by cation-exchange chromatography on SP-Sephadex. Further purification was obtained by extraction with n-butanol and anion-exchange chromatography on DEAE-cellulose. The resulting sialoglycoprotein fraction was free of lipids and nonsialylated glycoproteins and gave rise to four major periodic acid-Schiff staining bands when subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The fastest migrating protein on these gels with an apparent molecular weight of 19,000 was purified to homogeneity by gel filtration. The amino acid and sugar compositions of these materials are reported. The protein moiety is rich in serine, threonine, and hydrophobic amino acids and the carbohydrate moiety is high in sialic acid and N-acetylgalactosamine. Most of the carbohydrate is linked O-glycosidically to serine and threonine residues, as shown by susceptibility to base-catalyzed β-elimination and concomitant reduction of serine and threonine to alanine and α-aminobutyric acid and of N-acetylgalactosamine to N-acetylgalactosaminitol in the presence of reducing agents. The significance of these data in light of the known role of the rat erythrocyte membrane sialoglycoproteins in erythropoiesis is discussed. The properties of the rat erythrocyte membrane sialoglycoproteins are compared to those of other species.     

Studies on the role of goat heart galectin-1 as an erythrocyte membrane perturbing agent

Galectins are β-galactoside binding lectins with a potential hemolytic role on erythrocyte membrane integrity and permeability. In the present study, goat heart galectin-1 (GHG-1) was purified and investigated for its hemolytic actions on erythrocyte membrane. When exposed to various saccharides, lactose and sucrose provided maximum protection against hemolysis, while glucose and galactose provided lesser protection against hemolysis. GHG-1 agglutinated erythrocytes were found to be significantly hemolyzed in comparison with unagglutinated erythrocytes. A concentration dependent rise in the hemolysis of trypsinized rabbit erythrocytes was observed in the presence of GHG-1. Similarly, a temperature dependent gradual increase in percent hemolysis was observed in GHG-1 agglutinated erythrocytes as compared to negligible hemolysis in unagglutinated cells. The hemolysis of GHG-1 treated erythrocytes showed a sharp rise with the increasing pH up to 7.5 which became constant till pH 9.5. The extent of erythrocyte hemolysis increased with the increase in the incubation period, with maximum hemolysis after 5 h of incubation. The results of this study establish the ability of galectins as a potential hemolytic agent of erythrocyte membrane, which in turn opens an interesting avenue in the field of proteomics and glycobiology.