The isolation and characterization of the glycopeptides from horseradish peroxidase isoenzyme C

Effect of high hydrostatic pressure on activity, thermal stability and structure of horseradish peroxidase

The mechanism of the high hydrostatic pressure (HHP) effect on horseradish peroxidase (HRP) is still unclear. The activity, thermal stability and structural changes of HRP after HHP treatments were studied in this work. Compared with the untreated sample, the enzyme activity reduces by 36% after 800 MPa processing. The results indicated that the conformation of the enzyme active center changes under pressure. Furthermore, HHP also changes the conformation of disulfide bonds and some secondary structures in HRP. These structural and conformational changes induce decreased activity. In addition, differential thermal scanning (DSC) results showed that the thermal denaturation temperature decreased from 103.74 °C to 85.78 °C after pressure treatment, suggesting HRP molecules formed large aggregates after pressure treatment. In this study, the interaction mechanism between pressure and enzyme was studied as well, and the results can provide some guidance for the application of HHP technology in fruit and vegetable products processing.

Immobilization of water-soluble HRP within poly-N-isopropylacrylamide microgel particles for use in organic media

In the present work, the immobilization of enzymes within poly-N-isopropylacrylamide (p-NIPAM) microgels using the method of solvent exchange is applied to the enzyme horseradish peroxidase (HRP). When the solvent is changed from water to isopropanol, HRP is embedded within the polymer structure. After the determination of the immobilized amount of enzyme, an enhanced specific activity of the biocatalyst in isopropanol can be observed. Karl Fischer titration is used to determine the amount of water within the microgel particles before and after solvent exchange, leading to the conclusion that an "aqueous cage" remains within the polymer structure. This represents the driving force for the immobilization due to the high affinity of HRP for water. Beside, confocal laser scanning microscopy (CLSM) images show that HRP is located within the microgel network after immobilization. This gives the best conditions for HRP to be protected against chemical and mechanical stress. We were able to transfer a water-soluble enzyme to an organic phase by reaching a high catalytic activity. Hence, the method of solvent exchange displays a general method for immobilizing enzymes within p-NIPAM microgels for use in organic solvents. With this strategy, enzymes that are not soluble in organic solvents such as HRP can be used in such polar organic solvents.

Horseradish peroxidase: modulation of properties by chemical modification of protein and heme

Horseradish peroxidase (HRP) is one of the most studied enzymes of the plant peroxidase superfamily. HRP is also widely used in different bioanalytical applications and diagnostic kits. The methods of genetic engineering and protein design are now widely used to study the catalytic mechanism and to improve properties of the enzyme. Here we review the results of another approach to HRP modification-through the chemical modification of amino acids or prosthetic group of the enzyme. Computer models of HRPs with modified hemes are in good agreement with the experimental data.

Structural stabilization and functional improvement of horseradish peroxidase upon modification of accessible lysines: experiments and simulation

Horseradish peroxidase (HRP) is an important heme enzyme with enormous medical diagnostic, biosensing, and biotechnological applications. Thus, any improvement in the applicability and stability of the enzyme is potentially interesting. We previously reported that covalent attachment of an electron relay (anthraquinone 2-carboxylic acid) to the surface-exposed Lys residues successfully improves electron transfer properties of HRP. Here we investigated structural and functional consequences of this modification, which alters three accessible charged lysines (Lys-174, Lys-232, and Lys-241) to the hydrophobic anthraquinolysine residues. Thermal denaturation and thermoinactivation studies demonstrated that this kind of modification enhances the conformational and operational stability of HRP. The melting temperature increased 3 degrees C and the catalytic efficiency enhanced by 80%. Fluorescence and circular dichroism investigations suggest that the modified HRP benefits from enhanced aromatic packing and more buried hydrophobic patches as compared to the native one. Molecular dynamics simulations showed that modification improves the accessibility of His-42 and the heme prosthetic group to the peroxide and aromatic substrates, respectively. Additionally, the hydrophobic patch, which functions as a binding site or trap for reducing aromatic substrates, is more extended in the modified enzyme. In summary, this modification produces a new derivative of HRP with enhanced electron transfer properties, catalytic efficiency, and stability for biotechnological applications.

Horseradish peroxidase binding to intestinal brush-border membranes of Cyprinus carpio. Identification of a putative receptor

Morphologic studies have shown that the classic endocytosis tracer horseradish peroxidase (HRP) is actively internalized by vesicular transport in the carp intestine, suggesting the existence of specific binding sites in the apical membrane of enterocytes. The aim of the present study was to develop an in vitro binding assay using isolated carp intestinal brush-border membranes (BBM) to demonstrate and characterize these specific HRP binding sites. The results obtained show that HRP binding to BBM exhibits a saturable mode and high affinity (K(d) = 22 nM). In addition, HRP binding sites are highly enriched in BBM compared to basolateral membranes. On the other hand, HRP interaction with these sites is apparently of an ionic character because binding increased concomitantly with decreasing NaCl concentrations in the assay, reaching a maximum in the absence of NaCl. Other proteins that are also internalized in carp intestine did not significantly inhibit HRP binding to BBM. A lectin-type of interaction was discarded because neither manan nor ovoalbumin inhibited HRP binding. Proteinase K treatment of BBM reduced HRP binding by 70%, suggesting a proteic nature for this binding site. Finally, ligand blotting assays showed that HRP binds specifically to a 15.3-kDa protein. Taken together, these results are consistent with the existence of a functional receptor for HRP in carp intestinal mucosa that could mediate its internalization.

Apohorseradish peroxidase unfolding and refolding: intrinsic tryptophan fluorescence studies

The unfolding and refolding of apohorseradish peroxidase, as a function of guanidinium chloride concentration, were monitored by the intrinsic fluorescence intensity, polarization, and lifetime of the single tryptophan residue. The unfolding was reversible and characterized by at least three distinct stages-the intensity and lifetime data, for example, were both characterized by an initial increase followed by a decrease and then a plateau region. The lifetime data, in the absence and presence of guanidinium chloride, were heterogeneous and fit best to a model consisting of a major Gaussian distribution component and a minor, short discrete component. The observed increase in intensity in the initial stage of the unfolding process is attributed to the conversion of this short component into the longer, distributed component as the guanidinium chloride concentration increases. Our results clarify and amplify previous studies on the unfolding of apohorseradish peroxidase by guanidinium chloride.

Heterogeneity of glycans at each N-glycosylation site of horseradish peroxidase

The tryptic glycopeptides of horseradish peroxidase isozyme c (HRPc) were studied by methylation linkage analysis, exoglycosidase degradation, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDITOFMS). Over 90% of the predicted tryptic peptides and glycopeptides of HRPc could be identified in the unfractionated digest. Four glycans, namely (Xyl)Man3(Fuc)GlcNAc2 (major species), (Xyl)Man2(Fuc)GlcNAc2, (Xyl)Man3GlcNAc2, and Man3(Fuc)GlcNAc2 (minor species), were observed at all of the N-glycosylation sites and account for greater than 95% of the carbohydrate. Other members of this glycan family, namely (Xyl)xManm(Fuc)f GlcNAc2 (x = 0 or 1, f = 0 or 1, m = 4, 5, 6, or 7), account for the rest of the glycans. Only traces of high mannose-type glycans were detected in HRPc. Two sites, namely those at Asn-57 and Asn-267, were found to be more heterogeneous than the sites at Asn-13, Asn-158, Asn-186, 198 (doubly glycosylated peptide), Asn-214, and Asn-255. Two of the glycopeptides were observed as part of disulfide-linked species. MALDITOFMS confirmed the N-glycosylation sites previously reported [K.G. Welinder, Eur. J. Biochem., 96 (1979) 483-502] and was used to determine the heterogeneity of the glycan pool at each site.

The generation and characterization of a rat neural cell line overexpressing the alpha2,6(N) sialyltransferase

In order to examine the effects of altered protein sialylation on neural cell function, B104 rat neuroblastoma cells were stably transfected with the cDNA coding for alpha2,6(N) sialyltransferase (ST(6)N). Lectin blot analysis of the clones demonstrated an increase in staining of the Sambucus nigra lectin, which detects alpha2,6 linked sialic acid, in parallel with enzyme activity. There was a concomitant decrease in staining by the Maackia amurensis lectin which labels alpha2,3-linked sialic acid, indicating that the individual sialyltransferase enzymes may compete for penultimate galactose acceptor sites. While there was an initial increase in protein-bound sialic acid in parallel with enzyme activity, the sialylation of the cells was demonstrated to be saturable. There was an inverse relationship between cell adhesion to a fibronectin substrate and ST(6)N activity suggesting that the negatively charged sugar acts to modulate cell-substrate interaction. These cells will provide an ideal model system with which to further investigate the effect of altered sialic acid on neural cell function.

Glycans of higher plant peroxidases: recent observations and future speculations

Plant peroxidases are composed of a peptide and associated heme, calcium and glycans. The 3D structure of the major cationic peanut peroxidase has revealed the sites of the heme and calcium. But the diffraction of the glycans was not sufficient to show their structure. This review presents research that has been executed to obtain putative glycans and their binding sites, and to gain an indirect insight into these glycans. It also offers approaches that will be used to determine the function of the glycans on the peanut peroxidase. Some comparisons are made with other plant glycoproteins including peroxidases from plants other than peanut.

Heterogeneity of the covalent structure of the blue copper protein umecyanin from horseradish roots

The covalent structure of umecyanin has been determined by a combination of classical Edman degradation sequence analysis and plasma desorption, laser desorption, and electrospray ionization mass spectrometry. The preparation appeared to contain two isoforms having either a valine (75%) or an isoleucine (25%) residue at position 48. The polypeptide chain of 115 amino acids is strongly heterogeneous at its C-terminal end as a result of proteolytic cleavages at several places within the last 10 residues. The major fraction of the umecyanin preparation is only 106 residues long. The C-terminal tail 107-115 contains mainly alanine and glycine residues and a single hydroxyproline residue. In the native protein there is a disulfide bridge between Cys 91 and Cys 57, but in the apoprotein there is a disulfide shift that involves Cys 91 and one of the four copper binding residues (Cys 85). The three other ligand binding residues are His 44, His 90, and Gln 95. This tetrad of amino acids is the same as occurs in other type 1 copper proteins from plants such as cucumber peeling cupredoxin and lacquer tree stellacyanin. The umecyanin isoforms are glycoproteins with a glycan core having the same carbohydrate composition as that of horseradish peroxidase, a fact that is convincingly supported thanks to the high accuracy of the electrospray mass spectrometric technique. We suggest that the glycan may play a role in the association of the protein to the cellular membrane, but the precise functional role of umecyanin remains to be determined. We also discuss the evolutionary position of umecyanin in relation to the type 1 copper proteins in general.

A step towards understanding the folding mechanism of horseradish peroxidase. Tryptophan fluorescence and circular dichroism equilibrium studies

The guanidinium chloride denaturation/renaturation of the holo- and apo-horseradish peroxidase isoenzyme c (HRP) has been studied by fluorescence and circular dichroism spectroscopies. A distinct equilibrium intermediate of the apoprotein could be detected at low concentrations of guanidinium chloride (0.5 M). This intermediate has a secondary structure content like that of the native protein but a poorly defined tertiary structure. Renaturation of the apo-HRP is reversible and 100% activity could be obtained after addition of a twofold excess of free haem. The denaturation of the holo-HRP is more complex and occurs in two distinct steps; unfolding of the protein backbone and loss of the haem. The denatured protein folds back to its native conformation but the incorporation of the haem occurs only after the secondary structure is formed. Ca2+ appears to be important for the stability of the protein as the apo-HRP is more resistant to denaturation in the presence of Ca2+. The free-energy change during unfolding of the apo-HRP was determined in the absence and presence of Ca2+ and found to be 9.2 kJ/mol and 16.7 kJ/mol, respectively. The importance of Ca2+ to the protein stability was also supported by studies on the loss of the haem from the protoporphyrin-IX-apo-HRP complex.

The (1----3)-linked alpha-L-fucosyl group of the N-glycans of the Wistaria floribunda lectins is recognized by a rabbit anti-serum

An increasing number of plant glycoproteins have been shown to possess a characteristic N-glycan component containing a beta-(1----2)-linked D-xylose unit on the core beta-D-mannose unit, and an alpha-(1----3)-linked L-fucose unit on the asparagine-linked 2-acetamido-2-deoxy-D-glucose unit. Wistaria floribunda seeds have two distinct lectins; the erythroagglutinin, WFA, and the lymphocyte mitogen, WFM. Earlier studies indicated that both lectins belong to such a class of glycoproteins. We now report the complete structural analysis of Pronase glycopeptides derived from WFA. On the basis of chemical treatment of the glycopeptides, carbohydrate composition and methylation analysis of fluorescein-labeled glycopeptides, and their susceptibility to specific exoglycosidases, the structure of the WFA glycan was found to be, alpha-D-Manp-(1----6)-[beta-D-Xylp-(1----2)]- [alpha-D-Manp(1----3)]-beta-D-Manp-(1----4)-beta-D-GlcpNAc-[ alpha-L- Fucp-(1----3)]-beta-D-Glcp-NAc-(1----N). Quantitative studies on the interaction of the original fluorescein-labeled glycopeptide and its specific degradation products with a rabbit anti-glycan antibody, developed against WFM, showed that the (1----3)-linked alpha-L-fucose unit is essential for interaction. Loss of the terminal alpha-D-mannosyl groups resulted in decreased, though detectable binding.

Purification of a new peroxidase catalysing the formation of lignan-type compounds

A novel peroxidase that catalyses the dimerization of ferulic acid or caffeic acid via oxidative coupling and formation of beta beta'-linkage to the lignan-type compounds 8,8'-bis(caffeic acid) or 8,8'-bis(ferulic acid) respectively was purified from the leaves of Bupleurum salicifolium. The enzyme, for which the name caffeate peroxidase is proposed, was purified 2700-fold. It is a glycoprotein and has an Mr of 38,000 as determined by gel filtration and SDS/PAGE. The Km values for ferulic acid and caffeic acid were 0.24 mM and for H2O2 0.04 mM with caffeic acid and 0.48 mM with ferulic acid. The purified peroxidase does not exhibit activity on other phenylpropanoids tested and has no detectable phenol oxidase or NADPH oxidase activity. The caffeate peroxidase could be involved in the biosynthesis of lignans.

Mannose-sensitive HRP endocytosis by the retinal pigment epithelium

Mannose-sensitive endocytosis by rat retinal pigment epithelium (RPE) explants was characterized using the mannose-rich glycoprotein horseradish peroxidase (HRP). The number of HRP-containing endosomes in the RPE was morphologically quantitated by light microscopy while the amount of HRP ingested was biochemically quantitated by enzyme assay. HRP internalized via a mannose-sensitive receptor was differentiated from fluid-phase uptake in competitive inhibition studies using D-mannose. Morphological results showed that most HRP-containing endosomes formed within the first 15 min of incubation and showed little increase in number during 4 hr of continued incubation with HRP. In contrast, the biochemical assay showed a steady increase in the amount of HRP in RPE endosomes measured over time. The addition of 10 mM D-mannose to the incubation medium was associated with a significant decrease in both the number of HRP-containing endosomes and the amount of HRP ingested by RPE explants. Values indicate that half of the total uptake of HRP is mediated by a mannose-sensitive receptor while the balance is ingested via non-specific fluid-phase endocytosis.

Competition between ligands of glycosyltransferases and horseradish peroxidase for binding sites on intracellular and plasma membranes of HeLa cells. Application of a micro-method for the semi-quantitation of surface-bound HRP

A micro-method for the semi-quantitation of surface-bound horseradish peroxidase (HRP) was developed and was applied to study the competition between ligands of glycosyltransferases and HRP for binding sites on the surface of HeLa cells. Dried coverslip cultures of HeLa cells, fixed in methanol, were placed on 0.3 ml of the incubation medium on parafilm and were incubated for 45 min at 37 degrees C. The incubation medium contained HRP, lysozyme and Ca2+ in HEPES buffer, pH 7.2. After washing, the cells were incubated for 60 min at 37 degrees C in HEPES buffer containing 20 mM Ca2+. After this treatment, the plasma membranes showed a strong cytochemical reaction for HRP. Most of the HRP was released into buffer solution during a 5 h incubation at 37 degrees C in the absence of Ca2+, and was measured by spectrophotometry. The addition of 20 mM Ca2+ to the buffer solution prevented the release of most of the HRP from the plasma membranes thus showing that the binding of HRP required Ca2+. Ligands of glycosyltransferases were added to the incubation medium with HRP. The amount of HRP released from the cells decreased in relation to the competing potency and concentration of these ligands. The method was applied to estimate the concentration of some ligands of galactosyltransferase and sialyltransferase that caused a 50% decrease in the release of previously-bound HRP. CMP-neuraminic acid and gangliosides showed a higher competing potency to the surface binding of HRP than UDP-galactose and chitotriose. The spectrophotometric analysis was correlated (on duplicate samples) with cytochemical observations.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental cell death: morphological diversity and multiple mechanisms

Physiological cell death is a widespread phenomenon in the development of both vertebrates and invertebrates. This review concentrates on an aspect of developmental cell death that has tended to be neglected, the manner in which the cells are dismantled. It is emphasized that the dying cells may adopt one of at least three different morphological types: "apoptotic", "autophagic", and "non-lysosomal vesiculate". These probably reflect a corresponding multiplicity of intracellular events. In particular, the destruction of the cytoplasm in these three types appears to be achieved primarily by heterophagy, by autophagy and by non-lysosomal degradation, respectively. The various mechanisms underlying both nuclear and cytoplasmic destruction are reviewed in detail. The multiplicity of destructive mechanisms needs to be born in mind in studies of other aspects of cell death such as the signals which trigger it, since different signals probably trigger different types of cell death.

Enzymatic generation of triplet acetone by deglycosylated horseradish peroxidase

A study of the effects of deglycosylation of horseradish peroxidase on protein conformation, as well as on its catalytic activity of oxidation of isobutyraldehyde or its enol form to triplet acetone and formic acid, was performed. The loss of carbohydrates leads to structural modifications of this enzyme. This is confirmed by a change in the circular dichroism spectrum, an increase in tryptophan's environment polarity, and a loss of the chiral specificity toward D- and L-tryptophan. Deglycosylation does not destroy either the peptide backbone or the amino acid residues and does not affect the heme group content of the protein. The rates of oxygen uptake and light emission observed when horseradish peroxidase oxidizes isobutyraldehyde or the trimethylsilyl enol ether form of the latter are reduced when the enzyme is 70% deglycosylated. Concomitantly, the acting deglycosylated enzyme becomes inactivated during the course of the reaction. It appears that the carbohydrate moiety plays an important role in the protection of the peroxidase from damaging effects induced by triplet acetone and in the stabilization of the three-dimensional structure of this enzyme.

Endocytosis and autophagy in dying neurons: an ultrastructural study in chick embryos

In an effort to understand naturally occurring neuronal death in the developing isthmo-optic nucleus, we have accentuated one of its most probably causes, failure to receive adequate trophic maintenance from the axonal terminal zone in the retina, and have studied the dying neurons ultrastructurally. Retrograde trophic maintenance was blocked by means of intraocularly injected colchicine, which caused all the isthmo-optic neurons to die by just one of the two or more kinds of cell death that they undergo during normal development. The present paper deals with the very prominent cytoplasmic aspects of this kind of cell death, notably the uptake of exogeneous horseradish peroxidase and autophagy. There were also nuclear changes, which are dealt with mainly in the accompanying paper (Clarke and Hornung, J. Comp. Neurol. 283:438-449,'89). Numerous cytoplasmic vacuoles occurred in both soma and dendrites, and they were of three main kinds, of which the smallest (less than 0.5 microns diameter) had unstructured contents, whereas the larger two (1-2 microns and 2-7 microns) were secondary lysosomes (mostly residual bodies). Intravascularly injected horseradish peroxidase labeled all three kinds of vacuole but not the free cytoplasm, indicating that the uptake was by endocytosis rather than by leakage through holes in the membrane, as is confirmed by our failure to detect any such holes. We suspect that the smallest vacuoles are the primary endosomes, that these subsequently fuse with vacuoles of the intermediate kind, and that the largest vacuoles are formed by the fusion of these latter. The purpose of the endocytosis may be to channel the plasma membrane piecemeal into the lysosomes for destruction.

Sperm peroxidases and their possible role as glycoprotein-containing Con A and wheat germ lectin receptors

Peroxidases have been detected in the membrane of the ejaculated normal spermatozoon; their distribution on the different zones of the gamete has been determined. This distribution is similar to that of the N-linked glycoprotein-containing oligosaccharides. Their resemblance and similarity to the plant peroxidases, which are glycoproteins with N-type oligosaccharides, suggest that the sperm peroxidases might be, at least partially, identical to concanavalin A (Con A) and wheat germ lectin glycoprotein-containing receptors.

Cytochemical detection of receptors specific for N-linked oligosaccharides of glycoproteins in the membrane of the human spermatozoon and their distribution in the different zones of that membrane

The horseradish peroxidase (HRP), a glycoprotein rich in mannose and N-acetylglucosamine residues has been used as a ligand to detect receptors for N-glycosidic linked oligosaccharides of glycoproteins in the human spermatozoon. Specific binding of HRP occurred to the membrane and the binding sites were visualized with 3,3'-diaminobenzidine-H2O2 (DAB-H2O2) reagent, and by fluorescence when the FITC-peroxidase was used. This specific binding was suppressed by alpha-D-methyl-mannoside and human chorionic gonadotropin, decreased by follicle stimulating and luteinizing hormones and slightly diminished by N-acetylglucosamine. The distribution of the N-linked oligosaccharide specific receptors for glycoproteins in the different zones of the membrane of the spermatozoon was determined by counting the spermatozoa labeled in those zones. The pattern of the distribution is similar to that found for N-linked oligosaccharides containing glycoproteins of the same membrane. The similarity of these distributions together with the general model for cell-to-cell recognition suggest that the sperm-egg interaction mechanism could consist of dual interactions by double binding receptors.

Concanavalin A binding sites on the surface of Drosophila melanogaster sperm: a fluorescence and ultrastructural study

The distribution of alpha-D-mannose/alpha-D-glucose terminal residues in the plasma membrane of Drosophila melanogaster spermatozoon has been investigated by fluorescence and electron microscopy using concanavalin A (Con A) labeling. The results indicate the presence of distinct domains on the sperm surface. Intense binding of Con A to the plasma membrane is highly restricted to the acrosomal region and to the endpiece of the tail. In the former, Con A receptors are not homogeneously distributed, suggesting the presence of microdomains in the acrosomal area. The main part of the tail contains very few Con A binding sites, which are confined to specific areas of the membrane. The sperm surface overlying the nucleus is completely negative. The labeling pattern is unchanged after storage in the female before fertilization. A preliminary analysis of the surface of mature oocytes using fluorochrome-conjugated horseradish peroxidase indicates that D-mannose binding molecules are specifically associated with the chorion of the micropyle anterior part, which might therefore be the site of a preliminary interaction between egg and spermatozoon.

Molecular characteristics of many hemoproteins: a survey of molecular weights, sedimentation coefficients, other molecular parameters and amino acid compositions

Data on molecular weights, sedimentation coefficients, other molecular parameters and amino acids compositions of many hemoproteins were collected from the literature and studied. The results of the survey gave a general view of the molecular characteristics of hemoproteins and also revealed the presence of various statistical correlations among the molecular parameters and amino acid compositions. Some of the correlations were found to be practically useful for the estimation of number of heme per molecule, molecular weight or partial specific volume. Discussions were made on the possible structural basis of the molecular characteristics of hemoproteins.

Receptor-mediated uptake of horseradish peroxidase in innervated and denervated skeletal muscle

The in vitro uptake of [3H]inulin and horseradish peroxidase (HRP) has been studied in innervated and 6 days denervated extensor digitorum longus muscle of the mouse. Both markers were taken up at a higher rate in denervated muscle. The increase in uptake after denervation was, however, larger for HRP than for [3H]inulin. After 2 h incubation at 37 degrees C, pH 7.3, in the presence of equimolar concentrations of HRP and [3H]inulin (approx. 2.1 microM), the uptake of HRP was approx. 8 times as great as the uptake of [3H]inulin in the same innervated muscles. In denervated muscle the HRP uptake was approx. 19 times as great as the [3H]inulin uptake in the same muscles. Various possible explanations of these differences in uptake have been considered and tested experimentally. [3H]Inulin uptake in skeletal muscle has previously been shown to obey bulk kinetics. The present investigation shows the HRP uptake to obey saturation kinetics. The HRP uptake shows dependency on divalent cations and is reduced if incubation is carried out at pH 6.4. The uptake of HRP, when used at a low, non-saturating concentration (10 micrograms/ml approx. 0.25 microM), is inhibited greater than or equal to 60% by yeast mannan (0.1 mg/ml), ribonuclease B (0.1 mg/ml, approx. 7.4 microM), mannose (30 mM), monodansylcadaverine (1 mM), chloroquine (100 microM), trifluoperazine (25 microM) or maleic acid (2 mM). It is concluded that HRP is taken up in innervated and denervated skeletal muscle by a process of receptor-mediated endocytosis and that this uptake is under neurotrophic control.

Protein blotting: detection of proteins with colloidal gold, and of glycoproteins and lectins with biotin-conjugated and enzyme probes

Methods to detect "native" proteins immobilized on nitrocellulose membranes in spot tests or on blots prepared from polyacrylamide slab gels after electrophoretic separation are described. Gold sols were found to be useful as general stains for proteins: They are polychromatic, yield an indelible record, and are complementary to india ink as protein stains because these two stains have different sensitivities for a number of proteins tested. For detection of wheat germ lectin (WGL)-binding glycoproteins, avidin-peroxidase was an effective enzyme probe, because the glycoportion of the avidin moiety possesses binding affinity to WGL. Glycocomponents in human parotid saliva were detected with this probe and with the following biotin-conjugated lectins as intermediary probes: soybean lectin, Bandeiraea simplicifolia lectin, Lotus tetragonolobus lectin, and kidney bean lectin. Autoclaving blots prior to probing eliminated endogenous peroxidase activity. Concanavalin A and WGL were separated by isoelectric focusing and detected on blots with horseradish peroxidase and avidin-peroxidase, respectively. The versatility of the biotin/avidin system was used to detect other lectins on similar blots using biotin-conjugated glycoproteins as intermediary probes: Helix pomatia lectin and B. simplicifolia lectin were detected with biotinyl neoglycoproteins, and kidney bean lectin with biotin-conjugated components of parotid saliva.

Phaseolus vulgaris phytohemagglutinin contains high-mannose and modified oligosaccharide chains

Phytohemagglutinin, the major lectin in the seeds of the common bean Phaseolus vulgaris L., was isolated by affinity chromatography from cotyledons of nearly mature seeds and from developing cotyledons labeled with [(3)H]glucosamine, [(3)H]mannose or [(3)H]fucose. The protein was subjected to exhaustive proteolysis and the carbohydrate composition of the resulting glycopeptides examined. Two classes of oligosaccharide side-chains were found. The sidechains of the first class are of the high-mannose type, containing two residues of N-acetylglucosamine and 8 or 9 mannose residues. The sidechains of the second class are of the modified type containing N-acetylglucosamine, mannose, fucose, xylose in molar ratios of 2:3.8:0.6:0.5. Two-dimensional gel electrophoresis shows that phytohemagglutinin can be fractionated into seven different glycosylated polypeptides, and that each one contains at least one modified oligosaccharide chain. The results indicate that most glycosylated polypeptides probably contain one chain of each class. The carbohydrate composition of the two types of chains is similar to that found in other plant glycoproteins, but this is the first report of a plant glycoprotein with both highmannose and modified oligosaccharides on the same polypeptide chain.

Detection of neutral and aminosugars from glycoproteins and polysaccharides as their alditol acetates

A new method for the preparation and separation of alditol acetates from neutral sugars has been applied to aminosugars. Reduced aminosugars were rapidly acetylated using 1-methylimidazole as the catalyst without removal of borate formed during reduction. The alditol acetates were separated by glass capillary gas chromatography on Silar 10C. The alditol acetates of aminosugars had retention times much longer than those of neutral sugars. However, the alditol acetates of the deamination products of aminosugars had shorter retention times and were resolved from those of neutral sugars. This method was used for the simultaneous detection of neutral and aminosugars in acid hydrolysates of chitin and the glycoproteins, ovalbumin and peroxidase.

Competition between glycoprotein hormones and horseradish peroxidase for mannose-specific binding sites in cells of endocrine organs

Mannose-specific binding sites for horseradish peroxidase (HRP) were studied in paraformaldehyde-fixed, frozen sections of endocrine organs by a cytochemical method reported previously. In the testis, HRP was bound to interstitial cells, probably macrophages, and to sites extending along the surface of spermatozoa in the seminiferous tubules. In the epididymis, cells in the connective tissue, probably fibroblasts or macrophages, showed the specific reaction. In the ovaries, the reaction for lectin-bound HRP was observed in connective tissue cells of the theca externa, and in the mucosa of the uterus, binding of HRP occurred to many fibroblasts. The glycoprotein was also bound to cells in the connective tissue of the thyroid, probably mast cells, as well as to endothelial cells in the adrenal medulla and cortex. In all cases, the binding reaction required Ca2+ and was suppressed by mannose or mannan. Partially purified and highly purified preparations of glycoprotein hormones [ovine follicle-stimulating hormone, ovine luteinizing hormone, bovine thyroid-stimulating hormone, and human chorionic gonadotropin] as well as bovine thyroglobulin and yeast invertase competed with the binding of HRP to all the cells mentioned thus showing that the hormones were bound to the same sites as HRP. When 1 microM HRP was present in the incubation medium, the addition of 15-25 microM of highly purified hormones almost suppressed the reaction for lectin-bound HRP and competitive effects could be observed at even lower concentrations of the hormones.

Role of carbohydrate as an antigenic determinant of a glycoprotein from rye-grass (Lolium perenne) pollen

The carbohydrate component of Glycoprotein 2 (12% carbohydrate) from rye-grass (Lolium perenne) pollen has saccharide sequences that contribute to its antigenicity. Radioimmunoassay inhibition tests show that the antiserum to this glycoprotein cross-reacts with a number of other plant glycoproteins. In contrast, antiserum to another glycoprotein from rye-grass pollen, Glycoprotein 1 (5% carbohydrate), does not cross-react with any of the test glycoconjugates. Treatment of glycoproteins with sodium metaperiodate (0.02 M, 4 degree C, 6 h, in the dark) causes the loss of their ability to cross-react antigenically with Glycoprotein 2, and a loss of capacity to bind 125I-labelled concanavalin A. The cross-reactivity of this plant glycoprotein with other glycoconjugates imposes limitations on the interpretation of ultrastructural studies aimed at localizing a particular glycoprotein to a cellular site by using fluorescent or ferritin-labelled antisera. A radioimmunoassay inhibition technique for quantitative determination of the amounts of antigens in plants is also described.

Cytochemical detection of mannose-specific receptors for glycoproteins with horseradish peroxidase as a ligand

Horseradish peroxidase (HRP), a glycoprotein rich in mannose groups, was used as a ligand to detect receptors for glycoproteins in formalin-fixed, frozen sections of rat liver. Specific binding of HRP occurred to surface membranes of sinusoidal cells but not to those of parenchymal cells. The binding sites were visualized after the peroxidatic reaction in erythrocytes had been suppressed by methanol-H2O2 and phenylhydrazine, the latter reagent also decreasing the nonspecific background adsorption of HRP. Several factors influencing the reaction were studied systematically. The specific binding of HRP to sinusoidal cells was greatly decreased or abolished when tissue blocks were fixed for longer than 1-2 h in a cold 4% formaldehyde solution and the frozen sections subsequently treated for 30 min in cold methanol. The specific binding of HRP increased when the concentration of HRP in the medium was increased from 10 microgram/ml to 40 microgram/ml, when the time of incubation with HRP was increased from 1 h to 4 h, or when the temperature of incubation with HRP was increased from 4 degrees C to 22 degrees C, the pH of the incubation medium was increased from 7.0 to 10.0. Little or no specific binding of HRP was observed in the absence of added Ca++. The binding of HRP was suppressed by 10 mM mannose or 0.004% mannan whereas the suppression of the binding reaction by galactose or galactan required 30-40 ties higher concentrations.

Amino acid sequence studies of horseradish peroxidase. Amino and carboxyl termini, cyanogen bromide and tryptic fragments, the complete sequence, and some structural characteristics of horseradish peroxidase C

Horseradish peroxidase C dominates quantitatively among the isoperoxidases of horseradish root and has an isoelectric point close to 9. It consists of a hemin prosthetic group, 2 Ca2+ and 308 amino acid residues, including 4 disulfide bridges, in a single polypeptide chain that carries 8 neutral carbohydrate side-chains. The molecular weight of the polypeptide chain is 33890. Assuming an average carbohydrate composition of (GlcNAc)2, Man3, Fuc, Xyl for each carbohydrate chain, the molecular weight of native horseradish peroxidase C is close to 44 000. Cyanogen bromide fragments of reduced and carboxymethylated apo-peroxidase were purified by a combination of gel filtration and isoelectric focusing in urea, and cystine-containing tryptic fragments of apo-peroxidase were purified by gel filtration followed by disulfide cleavage and rechromatography at the initial conditions. The present paper discusses (a) isoelectric points and charge distribution within the native protein, the apoprotein and the cyanogen bromide fragments, (b) a buried pyrrolidonecarboxylyl amino terminus, (c) heterogeneity at the carboxyl terminus, and (d) a possible domain structure, likely from partial tryptic digestion.

Thermal inactivation of a heat-resistant lipase produced by the psychotrophic bacterium Pseudomonas fluorescens

Lipase from Pseudomonas fluorescens was studied for thermostability at temperatures ranging from 100 C to 160 C. The heat treatments were in two media, and heating times necessary to inactivate 90% of the enzyme at constant temperature were extremely long even at high temperatures, e.g. 3.6 min at 140 C in nutrient broth and 2.0 min at 170 C in skim milk. The increments of temperature to reduce these heating times 90% were 37.0 C in nutrient broth and 38.9 C in skim milk. The lipase was inactivated only partly after 20 h at 20 C in 8 M urea, 6 M guanidine hydrochloride, and 1.0% sodium dodecyl sulfate. Four percent 2-mercaptoethanol showed no effect.

Plant glycoprotein biosynthesis. Uridine diphosphate N-acetyl-glucosaminyltransferase from horseradish root

A particulate enzyme preparation from horseradish root tissue was shown to catalyze the transfer of 2-acetamido-2-deoxy-D-[14C1]glucose from uridine diphosphate 2-acetamido-2-deoxy-D-[14C1]glucose to an exogenous acceptor molecule derived from horseradish peroxidase. The acceptor was produced from purified peroxidase by the action of a mixture of glycoside hydrolases covalently bound to Sepharose. The membrane preparation containing the transferase was purified approximately 12-fold by aqueous two phase distribution and by discontinuous sucrose density gradient centrifugation. Hydrolysis of the reaction product yielded glucosamine as the only radio-labeled substance. Precipitation of the reaction product by antiserum against peroxidase showed that the label was incorporated into peroxidase. The transferase utilized the acceptor most efficiently when only 12% of the 2-acetamido-2-deoxy-D-glucose was removed from the acceptor. The acceptor lost no accepting capabilities when heated to 100 degrees C for 3 min prior to assay. Trypsin treatment caused a 14% decrease in label incorporated while pronase treatment caused a 93% decrease,