Edilbert Van Driessche

Bacterial contamination of boar semen affects the litter size.

One hundred and fifteen semen samples were collected from 115 different boars from two farms in Cuba. The boars belonged to five different breeds. Evaluation of the semen sample characteristics (volume, pH, colour, smell, motility of sperm cells) revealed that they meet international standards. The samples were also tested for the presence of agglutinated sperm cells and for bacterial contamination. Seventy five percent of the ejaculates were contaminated with at least one type of bacteria and E. coli was by far the major contaminant, being present in 79% of the contaminated semen samples (n=68). Other contaminating bacteria belonged to the genera Proteus (n=31), Serratia (n=31), Enterobacter (n=24), Klebsiella (n=12), Staphylococcus (n=10), Streptococcus (n=8) and Pseudomonas (n=7). Only in one sample anaerobic bacteria were detected. Pearsons analysis of the data revealed that there is a positive correlation between the presence of E. coli and sperm agglutination, and a negative correlation between sperm agglutination and litter size. One-way ANOVA and post hoc Tukey analysis of 378 litters showed that the litter size is significantly reduced when semen is used that is contaminated with spermagglutinating E. coli above a threshold value of 3.5x10(3)CFU/ml.

Thiourea: The antioxidant of choice for the purification of proteins from phenol-rich plant tissues☆

Metabisulfite, diethyldithiocarbamate, and thiourea are potent phenoloxidase inhibitors commonly used during the extraction of plant proteins. Their effects on several amino acid derivatives and peptides are reported. Important and pH-dependent changes are induced by metabisulfite in the uv-absorption spectrum of N-acetyltryptophanamide but not of N-acetyltyrosinamide. Similar spectral changes are also induced in tryptophanyl-containing peptides. Neither diethyldithiocarbamate nor thiourea modified the spectral properties of tryptophan or tyrosine. Cysteinyl groups are rapidly modified by diethyldithiocarbamate, especially in the lower pH range, but not by metabisulfite or thiourea. Diethyldithiocarbamate as well as metabisulfite interfere with cysteinyl groups. It is concluded that thiourea is the most appropriate reagent for use as a phenoloxidase inhibitor.

Prevalence of enterotoxigenic Escherichia coli virulence genes from scouring piglets in Zimbabwe

World-wide, enterotoxigenic Escherichia coli (ETEC) and verotoxigenic E. coli (VTEC)-induced diarrhea are economically important for porcine producers. Our aim was to investigate the prevalence of toxin and fimbrial genes among E. coli isolated from diarrheic piglets from randomly selected piggeries in Zimbabwe.We used multiplex PCR for screening STa, STb, LT, and Stx-2e toxins. Subsequently F4, F5, F6, F18 and F41 fimbriae genes were screened in toxin positive isolates. Toxin positive strains lacking tested fimbriae genes were characterized using transmission electron microscopy, agglutination and agglutination inhibition tests. Approximately 32% of the 1,984 isolates tested positive for STa, STb, LT or Stx-2e genes. Of these, approximately 81% had F4, F5, F6, F18 or F41 fimbriae genes. The remaining toxin positive strains lacked tested fimbriae genes and appeared to either express F1-like fimbriae, or lacked fimbriae. The data constitute an important framework for implementation of prevention measures, such as using relevant fimbriae-based vaccines against ETEC induced diarrhea or VTEC-induced edema.

Isolation and characterization of SAP and CRP, two pentraxins from Pangasianodon (Pangasius) hypophthalmus

From the serum of Pangasianodon hypophthalmus, two proteins were isolated by affinity chromatography on Sepharose and phosphorylcholine-Sepharose. Their binding on the affinity matrices critically depends on the presence of Ca2+ ions. N-terminal sequencing and sequencing of internal tryptic peptides identified the proteins as pentraxins and from their binding properties they are identified as SAP (serum amyloid P component) and CRP (C-reactive protein). Per ml serum, 36 microg SAP and 56 microg CRP was purified. Upon gel filtration, both the SAP and CRP elute as trimers of respectively 24 kDa and 28 kDa subunits. Both proteins are devoid of inter-chain disulfide bonds. Both SAP and CRP are glycosylated and agglutinate rabbit erythrocytes and pathogenic bacteria Edwardsiella ictaluri and Aeromonas hydrophila, but not Micrococcus lysodeikticus or Escherichia coli. Haemagglutination of SAP and CRP is inhibited by galactose (MIC = 1 mM) and by phosphorylcholine (MIC = 1-2 mM), respectively. Circular dichroism studies revealed that antiparallel beta-pleated sheets are dominating the secondary structure. Upon removing the Ca(2+) ions by EDTA, slight structural changes are observed by CD spectroscopy in the near-UV region. Immunodiffusion shows that P. hypophthalmus SAP and CRP do not cross-react.

Pig Heart Fumarase Contains Two Distinct Substrate-binding Sites Differing in Affinity

A eukaryotic fumarase is for the first time unequivocally shown to contain two distinct substrate-binding sites. Pig heart fumarase is a tetrameric enzyme consisting of four identical subunits of 50 kDa each. Besides the true substratesl-malate and fumarate, the active sites (sites A) also bind their analogs d-malate and oxaloacetate, as well as the competitive inhibitor glycine. The additional binding sites (sites B) on the other hand also bind the substrates and their analogsd-malate and oxaloacetate, as well asl-aspartate which is not an inhibitor. Depending on the pH, the affinity of sites B for ligands (K d being in the millimolar range) is 1–2 orders of magnitude lower than the affinity of sites A (of which K d is in the micromolar range). However, saturating sites B results in an increase in the overall activity of the enzyme. The benzenetetracarboxyl compound pyromellitic acid displays very special properties. One molecule of this ligand is indeed able to bind into a site A and a site B at the same time. Four molecules of pyromellitic acid were found to bind per molecule fumarase, and the affinity of the enzyme for this ligand is very high (K d = 0.6 to 2.2 μm, depending on the pH). Experiments with this ligand turned out to be crucial in order to explain the results obtained. An essential tyrosine residue is found to be located in site A, whereas an essential methionine residue resides in or near site B. Upon limited proteolysis, a peptide of about 4 kDa is initially removed, probably at the C-terminal side; this degradation results in inactivation of the enzyme. Small local conformational changes in the enzyme are picked up by circular dichroism measurements in the near-UV region. This spectrum is built up of two tryptophanyl triplets, the first one of which is modified upon saturating the active sites (A), and the second one upon saturating the low affinity binding sites (B).

The purification and physicochemical characterization of maize (Zea mays L.) isocitrate lyase.

A purification scheme is described for the glyoxylate cycle enzyme isocitrate lyase from maize scutella. Purification involves an acetone precipitation and a heat denaturation step, followed by ammonium sulfate precipitation and chromatography on DEAE-cellulose and on blue-Sepharose. The latter step results in the removal of the remaining malate dehydrogenase activity, and of a high molecular mass (62 kDa) but inactive degradation product of isocitrate lyase. Catalase can be completely removed by performing the DEAE-cellulose chromatography in the presence of Triton X-100. Pure isocitrate lyase can be stored without appreciable loss of activity at -70 degrees C in 5 mM triethanolamine buffer containing 6 mM MgCl2, 7 mM 2-mercaptoethanol, and 50% (v/v) glycerol, pH 7.6. Maize isocitrate lyase is a tetrameric protein with a subunit molecular mass of 64 kDa. Purity of the enzyme preparation was demonstrated by polyacrylamide gel electrophoresis in the presence of dodecylsulfate, in acid (pH 3.2) urea and by isoelectric focusing (pI = 5.1). Maize isocitrate lyase is devoid of covalently linked sugar residues. From circular dichroism measurements we estimate that its structure comprises 30% alpha-helical and 15% beta-pleated sheet segments. The enzyme requires Mg2+ ions for activity, and only Mn2+ apparently is able to replace this cation to a certain extent. The kinetics of the isocitrate lyase-catalyzed cleavage reaction were investigated, and the amino acid composition of the maize enzyme was determined. Finally the occurrence of an association between maize isocitrate lyase and catalase was observed. Such a multienzyme complex may be postulated to play a protective role in vivo.

Inhibitory action of spray dried blood plasma and whole egg powder on lectins in extracts of several legume seeds : a qualitative approach

Samples of seeds from eight legume species and Triticum vulgaris grains were extracted with buffer and lectin activity in the extracts was determined in haemagglutination experiments using normal or Pronase-treated rabbit erythrocytes. The effect of the addition of spray dried porcine and bovine plasma powder, whole egg powder, galactosides, whey powder and specific inhibitors (eg mannose, galactose, N-acetyl galactosamine, fetuin) on haemagglutination activity (HA) was determined. Plasma powders were potent inhibitors of HA in extracts of Pisum sativum, Vicia faba, Vicia sativa, Lens culinaris and Phaseolus vulgaris. HA in extracts of Lupinus sp and Phaseolus vulgaris was efficiently decreased by whole egg powder, while the lectin of Glycine max could only be inhibited by addition of galactosides, whole and defatted milk powder and whey powder. Inhibitors (plasma and whole egg powder and fetuin) were subjected to SDS-PAGE and Western blotting and blots were incubated with biotinylated lectins, except for Lupinus lectin. Results of the HA experiments were confirmed: lectins which were not influenced by inhibitory compounds in HA experiments also showed no binding with proteins of the blotted inhibitor. There were strong indications that lectins were not bound to the albumin fraction of the plasma powders. Results are discussed in view of future in vivo experiments.

Stability, Subunit Interactions and Carbohydrate-Binding of the Seed Lectin from Pterocarpus angolensis

From 1 kg of defatted Pterocarpus angolensis (mukwa tree) seed meal, 21.6 grams of an alpha,D-mannose/glucose-specific lectin can be purified on mannose-Sepharose. Relative affinities for several (oligo)saccharides and glycoproteins were studied by haemagglutination-inhibition. Gel filtration shows that the lectin exists as a dimer above pH 5 and as a monomer below pH 3.5. This is confirmed by studies on the release of lectin subunits that were adsorbed from solution to lectin monomers immobilized onto Eupergit-c. From the gel filtration patterns it is calculated that a residue with pK(a) of about 4.4 is involved in dimer dissociation. Titration of glutamic acids (E60, E209) is postulated to be involved. CD spectroscopy shows that the secondary structure of the lectin is unchanged between pH 1 and 12.5, and that the tertiary structure remains unchanged between pH 5 and 12. In the acid pH region, reversible spectral changes occur that may be due to the titration of one or more amino acids with a pK(a) value of 3.9-4.2, probably aspartic acid. These residues are implicated in sugar-binding but not in dimerization of the lectin. Only at pH 12.5, irreversible denaturation occurs. Mukwa lectin displays full carbohydrate-binding capacity between pH 4 and 12, as is concluded from ELLA (Enzyme Linked Lectin Assay) using ovalbumin and fetuin, and from binding of the same glycoproteins to immobilized lectin monomers. The lectin is rapidly and fully reversibly demetallized at pH 2.5 with 5 mM EDTA. The demetallized lectin is completely devoid of sugar-binding activity. Mukwa lectin is a very thermostable molecule (at least till 85 degrees C). However, addition of non-ionic detergents substantially lowers its thermostability.

Glycoprotein nature of α2-adrenergic receptors labeled with p-azido[3H] clonidine in calf retina membranes

α2,‐Adrenergic receptors in calf retina membranes can be specifically labeled with the tritiated agonist p‐azido[3H]clonidine. Saturation binding in the dark occurs with high affinity (1.3 ± 0.3 nM) to a single class of sites (1122 ± 67 fmol/mg protein). Irradiation of the membrane‐bound radioligand results in the labeling of a peptide band with an apparent size of 65 kDa and a characteristic pharmacological profile for an α2‐adrenergic receptor. The carbohydrate moieties of the α2‐receptor are characterized by lectin affinity chromatography and glycosidase treatment. The Nonidet P‐40‐solubilized, p‐azido[3H]clonidine‐labeled receptors are completely retained by Con A‐ as well as WGA‐Sepharose columns. Neuraminidase, α‐mannosidase and TFMS do not affect the electrophoretic mobility of the receptor on SDS‐PAGE whereas endoglycosidase F reduces the apparent size to 45 kDa.