Structural model of factors V and Va based on scanning transmission electron microscope images and mass analysis

Coagulation factor V (fV) is a single-chain glycoprotein (Mr 330,000; domain structure A1-A2-B-A3-C1-C2) that is activated to factor Va (fVa; Mr 174,000) by thrombin, which cleaves away the B domain leaving a heterodimeric structure composed of a heavy chain (A1-A2; Mr 94,000) and a light chain (A3-C1-C2; Mr 74,000). We analyzed the ultrastructure of scanning transmission electron microscope images of bovine and human fV, bovine fVa, and its constituent light chains and heavy chains. Factor V molecules had irregularly globular (10-12 nm) to oblong (8-14 nm) core structures which commonly displayed a peripheral satellite appendage of variable morphology attached to the core by a narrow stalk. Scanning transmission electron microscope mass analyses indicated that monomolecular bovine fV molecules had a mass of 322 +/- 45 kDa and human fV, 315 +/- 31 kDa. Factor Va molecules were irregular, globular (8-12 nm) structures that resembled the fV core structure, lacked the satellite appendage representing B domainal structures, and had a mass of 180 +/- 22 kDa. Our findings permit us to propose a structural model of fV suggesting the relative orientation of its closely associated light chain and heavy chain core components and indicating that these constituents remain associated in the transition from fV to fVa.     

A serine proteinase inhibitor isolated from Tamarindus indica seeds and its effects on the release of human neutrophil elastase

Proteinaceous inhibitors with high inhibitory activities against human neutrophil elastase (HNE) were found in seeds of the Tamarind tree (Tamarindus indica). A serine proteinase inhibitor denoted PG50 was purified using ammonium sulphate and acetone precipitation followed by Sephacryl S-300 and Sephadex G-50 gel filtration chromatographies. Inhibitor PG50 showed a Mr of 14.9 K on Sephadex G-50 calibrated column and a Mr of 11.6 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. PG50 had selective activity while cysteine proteinases (papain and bromelain) and serine proteinases (porcine pancreatic elastase and bovine chymotrypsin) were not inhibited, it was strongly effective against serine proteinases such as bovine trypsin and isolated human neutrophil elastase. The IC50 value was determined to be 55.96 microg.mL-1. PG50 showed neither cytotoxic nor haemolytic activity on human blood cells. After pre-incubation of PG50 with cytochalasin B, the exocytosis of elastase was initiated using PAF and fMLP. PG50 exhibited different inhibition on elastase release by PAF, at 44.6% and on release by fMLP, at 28.4%. These results showed that PG50 preferentially affected elastase release by PAF stimuli and this may indicate selective inhibition on PAF receptors.     

Presence of a Tetrahymena growth promoting activity in fetal bovine serum

Treatment of cultures of the ciliate Tetrahymena with fetal bovine serum (FBS) enhanced the rate of cell proliferation. The growth promoting activity was partially purified from FBS as a high Mr complex including four components with apparent Mr values of 180 kDa, 68 kDa, 60 kDa and 30 kDa by a 4-step procedure. The 180 kDa component was identified by amino acid sequencing as α2-macroglobulin. The addition of purified α2-macroglobulin from bovine plasma to cultures of Tetrahymena was also found to enhance the rate of cell proliferation. This report is the first dealing with the direct identification of a mammalian factor which promotes the growth of free-living protozoa.     

The gene sequence and some properties of protein H. A novel IgG-binding protein

The gene for protein H, a novel bacterial cell wall protein with specific affinity for human IgG Fc, was cloned from a group A Streptococcus and expressed in Escherichia coli. Recombinant E. coli cells produced two forms of a human IgG Fc-binding protein, one with an apparent Mr of 42 kDa in a periplasmic fraction and the other with an apparent Mr of 45 kDa in a mixed fraction of cytoplasms and membranes. Both 42-kDa and 45-kDa protein preparations similarly bound to human IgG1 to IgG4, human IgG Fc, and rabbit IgG, but not to IgG of mouse, rat, bovine, sheep, goat, and human IgA, IgD, IgE, and IgM. The complete nucleotide sequence of the cloned 1.8-kb DNA fragment was determined. An open reading frame encoded a hypothetical protein of 376 amino acid residues (Mr = 42,498). The N-terminal amino acid sequence, consisting of 41 residues, which was removed post-translationally had typical characteristics of Gram-positive bacterial signal peptides. Thus, the mature form of protein H was suggested to consist of 335 residues (Mr = 38,162). There were 3 repeated sequences consisting of 42 residues that were highly homologous to those of protein Arp, an IgA-binding streptococcal cell wall protein, and streptococcal M6 and M24 proteins. The C-terminal amino acid sequence consisting of 93 residues, directly following the repeated sequences, was also highly homologous to that of M6 and M24 proteins. No sequence homology was found between protein H and protein A or protein G, two other IgG-binding bacterial cell wall proteins.     

Demonstration of the specific binding of bovine transferrin to the human transferrin receptor in K562 cells: evidence for interspecies transferrin internalization

Specific binding of ferric bovine transferrin to the human transferrin receptor was investigated using K562 cells propagated in serum-free medium without transferrin supplemented with 10(-5) elemental iron. Affinity chromatography of solubilized extracts of K562 cells surface-labeled with 125I was performed using bovine transferrin- and human transferrin-Sepharose 4B resins. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of resin eluates reveal that bovine transferrin specifically binds a Mr = 188,000 protein which dissociates into a Mr = 94,000 protein under reducing conditions, a finding identical to what is seen with human transferrin. The Mr = 94,000 reduced protein isolated by bovine transferrin resin shows an identical one-dimensional partial proteolytic digestion map with that of the human transferrin receptor. Unlabeled bovine transferrin was shown to specifically compete 125I-labeled human transferrin from the human transferrin receptor on the surface of K562 cells at 4 degrees C in a similar manner as unlabeled human transferrin; however, approximately a 2,000-fold higher concentration of bovine ligand was required to achieve comparable competition (50% inhibition of binding). Indirect immunofluorescence cytolocalization of bovine transferrin in K562 cells grown in serum-free medium supplemented with ferric bovine transferrin reveal patterns similar to those seen for human transferrin (both focal perinuclear and diffuse cytoplasmic fluorescence). Monensin treatment results in a dramatic accumulation of bovine ligand in perinuclear aggregates, suggesting that it is recycled through the Golgi, as is human transferrin. K562 cells grown in serum-free medium supplemented with either 300 micrograms/ml of ferric human or ferric bovine transferrin were found to demonstrate superimposable growth curves.     

Properties of bovine nephritogenic antigen that induces anti-GBM nephritis in rats and its similarity to the Goodpasture antigen.

The nephritogenic antigen that induces antiglomerular basement membrane antibody-induced glomerulonephritis (anti-GBM nephritis) in rats was isolated from collagenase-solubilized bovine renal basement membranes. Purification was achieved using antibody-coupled affinity columns which were originally used for the purification of trypsin-solubilized nephritogenic antigen (Sado et al. 1984a). The nephritogenic antigen was a heteropolymer composed of P2 (Mr 28 kDa) and P3 (Mr 30 kDa) polypeptides as monomers and their dimers in sodium-dodecyl-sulfate (SDS) polyacrylamide gel electrophoresis. The P3 polypeptide was considered to be the nephritogenic epitope, since a fraction composed of the P2 polypeptide alone was not nephritogenic. The properties of the nephritogenic epitope were the same as those of the Goodpasture epitope (M2*), which is a noncollagenous domain of the alpha 3 chain of type IV collagen (Butkowski et al. 1985; Saus et al. 1988), indicating that the nephritogenic antigen is the same as the Goodpasture antigen.     

Interaction of eukaryotic tyrosyl-tRNA-synthetase with high molecular weight RNA

The affinity of eukaryotic tyrosyl-tRNA synthetases from bovine liver and from yeast for E. coli ribosomal RNA and synthetic polyribonucleotides has been studied by protein binding on the rRNA-Sepharose column and enzyme inhibition by high molecular weight RNAs. Tyrosyl-tRNA synthetase from bovine liver (Mr 2.59 kDa) was fully retained on the rRNA-Sepharose and eluted by buffer with 100 mM KCl. The functionally active modified form of bovine liver tyrosyl-tRNA synthetase obtained by endogenous limited proteolysis (Mr 2.38 kDa) partially maintains the affinity for rRNA and is eluted by 50 mM KCl. The highest rRNA-binding ability was revealed for yeast tyrosyl-tRNA synthetase eluted by 200 mM KCl. The E. coli tyrosyl-tRNA synthetase was not retained on rRNA-Sepharose. The aminoacylation activities of both bovine liver and yeast tyrosyl-tRNA synthetases were efficiently inhibited by rRNA and the inhibition was partially competitive in respect to tRNA(Tyr). At the same time the activities of proteolytically modified bovine tyrosyl-tRNA synthetase and E. coli tyrosyl-tRNA synthetase were not influenced by the addition of rRNA. Synthetic single- and double-stranded polyribonucleotides specifically inhibited the activity of bovine tyrosyl-tRNA synthetase to different extent. The inhibition degree of bovine liver tyrosyl-tRNA synthetase decreased in the order: poly (G) greater than poly (I) greater than poly (I).poly (C) greater than poly (G).poly (C) greater than poly (C) greater than poly (A). Poly (U) did not inhibit the activity of bovine liver tyrosyl-tRNA synthetase.     

Isolation of GTP-binding Gs-protein liberated from human erythrocyte membranes under the action of fluoride ions

Human erythrocyte membranes were incubated in the presence of sodium fluoride. After centrifugation at 30,000 g for 30 min the supernatant was able to stimulate the catalytic subunit of adenylate cyclase. The stimulatory factor was purified from the supernatant of fluoride-treated membranes by three subsequent chromatographic steps including DEAE-Sephacel ion-exchange chromatography in the absence of detergent, gel-filtration on Ultrogel AcA 44 in the presence of 1% sodium cholate and phenyl-Sepharose CL/4B hydrophobic chromatography. The final preparation showed approximately 120-fold purification in stimulatory activity over the initial extract and contained two polypeptides (Mr 42 kDa and 36 kDa). The stimulator activity of the preparation was inhibited by 60% by beta gamma-subunits of the GTP-binding protein of bovine brain membranes, G0. The data obtained suggest that the regulatory GTP-binding stimulatory protein of adenylate cyclase, GS, dissociates from human erythrocyte membranes as a result of fluoride-ion treatment.     

The bovine peripheral-type benzodiazepine receptor: a receptor with low affinity for benzodiazepines.

The density of bovine peripheral-type benzodiazepine receptors (PBR) in four tissues was highest in adrenal cortex. The adrenal cortex PBR cofractionated with a mitochondrial membrane marker enzyme and could be solubilized with intact ligand binding properties using digitonin. The membrane bound and soluble mitochondrial receptors were pharmacologically characterized and showed the rank order of potency to inhibit [3H]PK 11195 binding was PK 11195 greater than protoporphyrin IX greater than benzodiazepines (clonazepam, diazepam, or Ro5-4864). [3H]PK 11195 binding to bovine adrenal mitochondria was unaffected by diethylpyrocarbonate, a histidine residue modifying reagent that decreased binding to rat liver mitochondria by 70%. [3H]PK 14105 photolabeled the bovine PBR and the Mr was estimated under nondenaturing (200 kDa) and denaturing (17 kDa) conditions. These results demonstrate the bovine peripheral-type benzodiazepine receptor is pharmacologically and biochemically distinct from the rat receptor, but the receptor component photolabeled by an isoquinoline ligand has a similar molecular weight.     

Dermatan sulphate proteoglycan from human articular cartilage. Variation in its content with age and its structural comparison with a small chondroitin sulphate proteoglycan from pig laryngeal cartilage.

Low molecular mass proteoglycans (PG) were isolated from human articular cartilage and from pig laryngeal cartilage, which contained protein cores of similar size (Mr 40-44 kDa). However, the PG from human articular cartilage contained dermatan sulphate (DS) chains (50% chondroitinase AC resistant), whereas chains from pig laryngeal PG were longer and contained only chondroitin sulphate (CS). Disaccharide analysis after chondroitinase ABC digestion showed that the human DS-PG contained more 6-sulphated residues (34%) than the pig CS-PG (6%) and both contained fewer 6-sulphated residues than the corresponding high Mr aggregating CS-PGs from these tissues (86% and 20% from human and pig respectively). Cross-reaction of both proteoglycans with antibodies to bovine bone and skin DS-PG-II and human fibroblasts DS-PG suggested that the isolated proteoglycans were the humans DS-PG-II and pigs CS-PG-II homologues of the cloned and sequenced bovine proteoglycan. Polyclonal antibodies raised against the pig CS-PG-II were shown to cross-react with human DS-PG-II. SDS/polyacrylamide-gel analysis and immunoblotting of pig and human cartilage extracts showed that some free core protein was present in the tissues in addition to the intact proteoglycan. The antibodies were used in a competitive radioimmunoassay to determine the content of this low Mr proteoglycan in human cartilage extracts. Analysis of samples from 5-80 year-old humans showed highest content (approximately 4 mg/g wet wt.) in those from 15-25 year-olds and lower content (approximately 1 mg/g wet wt.) in older tissue (greater than 55 years). These changes in content may be related to the deposition and maintenance of the collagen fibre network with which this class of small proteoglycan has been shown to interact.     

Myosin isoforms and cell heterogeneity in vascular smooth muscle. I. Developing and adult bovine aorta

Monoclonal anti-smooth muscle (SM-E7, SM-F11, and BF-48) and anti-nonmuscle (NM-A9 and NM-G2) myosin antibodies, Western blotting, and immunocytochemical procedures were used to study myosin isoform composition and distribution in the smooth muscle (SM) cells of bovine aorta differentiating in vivo and in vitro. Two myosin heavy chain (MHC) isoforms were identified by SM-E7 in adult aorta: SM-MHC-1 (Mr = 205 kDa) and SM-MHC-2 (Mr = 200 kDa), respectively. When tested with the SM-F11 antibody, SM-MHC-2 isoform showed distinct antigenic properties compared to SM-MHC-1. Two bands of 205 and 200 kDa were also present in the aortic SM tissue from 3-month-old fetus and were equally recognized by the BF-48 antibody. The 200-kDa SM myosin isoform was labeled by SM-F11 but not by SM-E7, thus indicating the existence of a fetal-specific SM-MHC-2 isoform. At the cellular level, both developing and adult bovine aortic tissues showed the existence of distinct patterns of myosin isoform expression. Three or even more aortic cell populations are differently distributed in areas which appear as (1) a network of interconnecting sheet-like or compact tissue (early fetus) and (2) enriched of collagenous-elastic or muscular tissue (adult animal). In addition, the SM-MHC-2 isoform of the fetal type appears to be uniquely distributed in cultured SM cells grown in vitro from adult bovine aortic explants. Our data indicate that in bovine aorta (1) MHC isoform expression is developmentally regulated and (2) the distribution of myosin isoforms is heterogenous both among and within aortic cells. These findings may be related to the distinct physiological properties displayed by SM during vascular myogenesis.     

Identification of a human bone marrow-derived immunoenhancing factor, BDEF

In this report we describe the production and biological activity of human bone marrow-derived enhancing factor (BDEF). This factor is the constitutive product of cultured human BMC and could initially be recovered by ultrafiltration of cell-free BM supernatants to yield a crude fraction of Mr greater than 10,000 Da. This preparation can enhance the Ab response of human tonsillar cells, as well as murine spleen cells, to SRBC. HPLC fractionation of BM supernatants enriches for enhancing activity in a peak with an approximate Mr of 60 kDa. PAGE gel analysis reveals two protein bands which migrate to this area, one of 60 kDa, and a slightly smaller protein at 55 kDa. Antibodies generated against the above two proteins were shown to be specific by Western blotting and could recognize the native BM proteins as determined by ELISA. The antibodies were used to affinity purify the respective proteins, p60 and p55. The BM protein p60, but not p55, was able to enhance Ab synthesis in vitro and was also mitogenic for murine BMC and thymocytes. The addition of anti-p60 Ab to human tonsillar cells cultured with SRBC and human BDEF preparations resulted in abrogation of enhancement. These findings support the notion that the BM protein p60 is BDEF and that it may represent a novel enhancing molecule produced by normal human BM.     

Antioxidant properties of some different molecular weight chitosans

Chitosan, a cationic polysaccharide, is widely employed as dietary supplement and in pharmacological and biomedical applications. Although numerous studies have focused on its applications as pharmaceutical excipients or bioactive reagents, relationships between molecular weight (Mr) and biological properties remain unclear. The focus of this study was on the antioxidant properties of several Mr chitosans. We measured the ability of seven Mr chitosans (CT1; 2.8 kDa, CT2; 17.0 kDa, CT3; 33.5 kDa, CT4; 62.6 kDa, CT5; 87.7 kDa, CT6; 604 kDa, CT7; 931 kDa) to protect plasma protein from oxidation by peroxyl radicals derived from 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH). A comparison of the antioxidant action of high Mr chitosans (CT6–CT7) with that of low Mr chitosans (CT1–CT5) showed that low Mr chitosans (CT1–CT5) were more effective in preventing the formation of carbonyl groups in plasma protein exposed to peroxyl radicals. AAPH substantially increases plasma protein carbonyl content via the oxidation of human serum albumin (HSA). We also measured the ability of these chitosans to protect HSA against oxidation by AAPH. Low Mr chitosans (CT1–CT5) were found to effectively prevent the formation of carbonyl groups in HSA, when exposed to peroxyl radicals. Low Mr chitosans were also good scavengers of N-centered radicals, but high Mr chitosans were much less effective. We also found a strong correlation between antioxidant activity and the Mr of chitosans in vitro. These activities were also determined by using the ‘TPAC’ test. These results suggest that low Mr chitosans (CT1–CT3) may be absorbed well from the gastrointestinal tract and inhibit neutrophil activation and oxidation of serum albumin that is frequently observed in patients plasma undergoing hemodialysis, resulting in a reduction in oxidative stress associated with uremia.     

Intracellular and oligomeric forms of surfactant-associated apolipoproteins(s) A in the rat

Sulfhydryl-dependent oligomeric forms of the surfactant-associated apolipoprotein(s) A, obtained from particulate preparations of adult rat lung lavage, were characterized by immunoblot analysis and by silver staining of proteins separated by one- and two-dimensional SDS-polyacrylamide gel electrophoresis. Under non-reducing conditions, these proteins migrated as oligomers, Mr approx. 50-70, 115, 160 kDa and greater. The large oligomers were reduced to the apolipoprotein(s) A subunits by treatment with beta-mercaptoethanol; Mr 38 (A3), 32 (A2) and 26 kDa (A1), pI 4.2-4.8. Mr 50 kDa protein was composed of sulfhydryl-dependent homo-dimers of protein(s) A1 (Mr 26 kDa). 55 kDa protein was a hetero-dimer composed primarily of A1 and A2 (Mr 26 and 32 kDa). 62 kDa protein was composed of hetero-dimers of A3 and apolipoprotein A2 (Mr 38 and 32 kDa). 70 kDa protein was a homodimer composed of apolipoprotein A3 A3 (38 kDa). Larger molecular forms were composed primarily of 38 and 32 kDa and lesser amounts of 26 kDa. Treatment with endoglycosidase F reduced A2 and A3 to 26 kDa. Apolipoprotein A1 co-migrated with a protein of Mr 26 kDa immunoprecipitated from [35S]methionine-labelled Type II epithelial cells. Chymotryptic-tryptic peptide maps of apolipoproteins A1, A2 and A3 were identical, suggesting that apolipoproteins A3 and A2 arise through extensive glycosylation of apolipoprotein A1.     

Expression of bovine adrenodoxin and NADPH-adrenodoxin reductase cDNAs in Saccharomyces cerevisiae

Expression of both bovine adrenodoxin (ADX) and NADPH-adrenodoxin reductase (ADR) were examined in Saccharomyces cerevisiae. Three ADX and two ADR expression plasmids were constructed by inserting each of the corresponding cDNA fragments between the yeast alcohol dehydrogenase I promoter and terminator of the expression vector pAAH5N. Plasmids pAX and pMX contained the coding region for the precursor and mature ADX, respectively, while pCMX carried the mature ADX preceded by the mitochondrial signal of yeast cytochrome c oxidase subunit IV (COX IV). Similarly, pMR and pCMR coded for mature ADR without and with the mitochondrial signal of yeast COX IV, respectively. Transformed S. cerevisiae AH22[rho 0]/pAX cells produced the ADX precursor, while AH22[rho 0]/pMX and AH22[rho 0]/pCMX cells produced mature ADX (mat-ADX) and modified ADX (mat-COX/ADX), respectively. Mat-ADX and mat-COX/ADX were found mainly in the cytosolic and mitochondrial fractions, respectively, and showed cytochrome c reductase activity. AH22[rho+]/pMR and AH22[rho+]/pCMR cells produced mature ADR (mat-ADR) and modified ADR (mat-COX/ADR), respectively. Mat-ADR lacking the mitochondrial signal was found in the cytosolic fraction and exhibited cytochrome c reductase activity, while mat-COX/ADR was localized in the mitochondrial fraction, but showed no reductase activity. In an in vitro reconstituted system consisting of both mat-COX/ADX- and mat-ADR-containing fractions, bovine P450scc converted cholesterol into pregnenolone. Thus mat-COX/ADX and mat-ADR produced in the yeast can transfer electrons from NADPH to P450scc.     

The molecular structure and lubricating activity of lubricin isolated from bovine and human synovial fluids.

Lubricin was isolated from bovine ankle, metacarpophalangeal and knee and human knee synovial fluids. The lubricins isolated from the bovine joint fluids had the same amino acid and carbohydrate compositions, but differences were observed in the relative molecular masses. The Mr values of bovine metacarpophalangeal and ankle lubricin determined by light-scattering measurements were about 200 000, whereas values of 132 000 and 143 000 were obtained for the bovine knee lubricin. The human knee lubricin had a similar carbohydrate composition to bovine knee lubricin except for the higher glucosamine content, and the amino acid composition differed slightly. The human sample had a lower glutamic acid content and a leucine/isoleucine ratio of 2:1 compared with 1:1 in the bovine. The Mr value of the human knee lubricin (166 000) was also lower than that of the bovine metacarpophalangeal and ankle samples. The Mr value of the bovine knee lubricin determined by sedimentation-equilibrium measurements was 171 000. The length measurements determined by electron microscopy and also the sedimentation measurements showed considerable polydispersity and indicate that the degree of extension of lubricin molecules can vary. Friction measurements showed that the human knee synovial-fluid lubricin had equivalent lubricating ability in a test system in vitro to that observed for lubricin isolated from normal bovine synovial fluids. The lubricating ability of lubricin was concentration-dependent, and each lubricin sample was able to act as a lubricant in vitro in an equivalent manner to whole synovial fluid at concentrations that are thought to occur in vivo.     

Characterization of the major proteins of bovine seminal fluid by two-dimensional polyacrylamide gel electrophoresis

Recently, we demonstrated that the major proteins from bovine seminal plasma BSP-A1, -A2, -A3 and -30-kDa (collectively called BSP proteins) specifically interact with choline phospholipids. These proteins coat the surface of the spermatozoa after ejaculation and are believed to play an important role in membrane modifications occurring during capacitation. In this study we determined the isoelectric point (pl) and analysed the molecular heterogeneity of BSP proteins. Total protein from bovine seminal plasma (CBSP) and purified BSP proteins were iodinated using chloramine T. Samples were reduced, denatured, separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), and visualized by autoradiography. Analysis of CBSP proteins demonstrated the presence of polypeptides migrating in the pH range of 3.5–7.8 and at molecular weights (Mr) between 6 and 100 kDa. Many isoforms of each BSP protein were found when purified iodinated proteins were analysed by 2D-PAGE. BSP-A1 was found at a Mr of 16.5 kDa and in the range of pl of 4.7–5.0; BSP-A2 at 16 kDa and at a pl of 4.9–5.2; BSP-A3 at 15 kDa and at a pl of 4.8–5.2, and BSP-30-kDa at 28 kDa and at a pl of 3.9–4.6. Similar results were obtained with immunolocalization of BSP proteins after Western blot using specific antibodies. The treatment of purified iodinated BSP proteins with neuraminidase increased the pl of BSP-30-kDa to 4.8–5.0 and decreased its Mr to 25 kDa, but no change was observed for BSP-A1, -A2 and -A3. The treatment of BSP proteins with sulfatase or acid phosphatase modified neither their Mr nor their pl. Furthermore, when CBSP proteins were separated in 2D-PAGE and the gels stained for glycoproteins with dansyl hydrazine, BSP proteins were among the major glycoproteins found in the bovine seminal plasma. In conclusion, BSP proteins are acidic and have several isoforms. Furthermore, the heterogeneity of BSP-30-kDa is mainly due to its sialic acid content. © 1994 Wiley-Liss, Inc.     

Characterization of a novel gelatin-binding 21 kDa protein secreted by cultured adherent cells

A novel gelatin-binding 21 kDa protein was identified in the culture medium of fibroblastic and sarcoma cells by affinity chromatography on gelatin-Sepharose. Its affinity for gelatin was lower than that of the other gelatin-binding proteins, fibronectin and the 70 kDa protein, as judged by stepwise elution by urea and arginine. The protein bound also to spermine and to some extent to heparin but not to staphylococcal protein A, bovine serum albumin, concanavalin A or plain Sepharose 4B. In gel filtration chromatography the protein eluted in fractions differing from those of fibronectin and the Mr 70,000 protein and retained its ability to bind to gelatin-Sepharose, indicating that the binding was not mediated by the two other gelatin-binding proteins. It contains intrachain disulfide bridges, as judged by analysis under nonreducing and reducing conditions. The protein is composed of two major subtypes with pI values of 5.85-6.10 and 6.55-6.75. It was sensitive to trypsin but not to collagenase or thrombin. Antiserum was raised in rabbits against the gelatin-binding proteins isolated from serum-free conditioned fibroblast culture medium. The antiserum reacted with fibronectin, the Mr 70,000 protein and the Mr 21,000 protein in immunoprecipitation experiments. Absorption of the antiserum with human plasma fibronectin did not decrease its reactivity with the Mr 70,000 and 21,000 proteins. However, absorption with the Mr 70,000 protein abolished also the reactivity against the Mr 21,000 protein, suggesting immunological cross-reactivity. The protein was synthesized independently from the Mr 70,000 protein, as shown by pulse-chase labeling experiments of cells. The production of the Mr 21,000 protein in cultured cells was enhanced by transforming growth factor-beta.     

The presence of ATP + ubiquitin-dependent proteinase and multicatalytic proteinase complex in bovine brain

The presence of two distinct high-molecular-weight proteases with similar pH optima in the weakly alkaline region was shown in cytosol of the bovine brain cortex. They were separated by ammonium sulfate fractionation and each was further purified by DEAE-Sephacel Sephacryl S-300, DEAE-Cibacron Blue 3GA-agarose, heparin-agarose, and Sepharose 6B chromatography. The larger enzyme (Mr 1,400 kDa), which precipitates at 0–38% ammonium sulfate saturation, seems to be active in ATP+ubiquitin (Ub)-dependent proteolysis; it has low basal caseinolytic activity that is stimulated 3-fold by ATP, and when Ub is present ATP causes a 4.5-fold stimulation. A second proteinase was also found to be present (Mr 700 kDa) that precipitates at 38–80% ammonium sulfate saturation, is composed of multiple subunits ranging in Mr from 18 to 30 kDa, and degrades both protein and peptide substrates, demonstrating trypsin-, chymotrypsin- and cucumisin-like activities. Catalytic, biochemical, and immunological characteristics of this proteinase indicate that it is a multicatalytic proteinase complex (MPC), whose enzyme activity, in contrast to that of MPC from bovine pituitaries (1–3), is stimulated 1.7-fold by addition of ATP in the absence of ubiquitin at the early steps of purification; this property is lost during the course of further purification. Both proteinases are present in the nerve cells, since the primary chicken embryonic telencephalon neuronal cell culture extracts contain both ATP+Ub-dependent proteinase and MPC activities.Special issue dedicated to Dr. Paola S Timiras     

Alpha-galactoside-binding isolectins from wild jack fruit seed (Artocarpus hirsuta): purification and properties

Five isolectins with marked specificity for alpha-linked galactose were purified from the wild jack (Artocarpus hirsuta) seeds by affinity chromatography on cross-linked guar gum. They were composed of a glycosylated subunit A (Mr = 16 kDa) and a nonglycosylated subunit B (Mr = 11 kDa) in noncovalent association. The isolectins which eluted as a single peak of Mr 45 kDa on gel filtration in Biogel P-100 and in a TSK G-3000 SW high pressure column, were resolved into five peaks on electrophoresis at pH 4.5. Sodium dodecyl sulphate polyacrylamide gel electrophoreogram of the major isolectin band suggested that the isolectins may be the five possible tetrameric combinations of A and B subunits. The combined isolectins bound only two molecules of 4-methyl umbelliferyl alpha-D-galactoside with a binding constant of 4.75 x 10(4) M-1. The pH optimum of sugar binding was 7.0. The isolectins specifically bound to human IgG and IgA but not to IgM.