Effect of a one-off sporidesmin challenge on the milk production of dairy cows.

AIMS To investigate the effects on milk yield in lactating dairy cows of a single dose of sporidesmin, and to categorise the responses based on clinical signs and differing degrees of liver damage, as assessed by activities of γ-glutamyl transferase (GGT) and post-mortem liver histopathology. METHODS Adult lactating dairy cows (n=17) were given a single intra-ruminal dose of 0.24 mg/kg of sporidesmin dissolved in ethanol and diluted in water on Day 0; an additional three cows served as untreated controls. Weekly serum samples were collected between Days -14 and 42 and analysed for activities of GGT. Milk yields were measured daily over the same period. Cows were subjected to euthanasia due to severe clinical signs (n=2) or were slaughtered at the end of the trial. Samples of livers were examined histologically and were scored for lesions on a scale from 0 (normal) to 3 (severe). Based on GGT activities and clinical observations, cows that were treated with sporidesmin were categorised as non-responders (no clinical signs and normal GGT), subclinical (elevated GGT and no clinical signs) or clinical. Outcomes were compared between these three groups and control cows using generalised additive models. RESULTS Seven cows were classified as clinical, and had median liver scores of 22 (95% CI=20.6-23.4), six were subclinical with median liver scores of 8.7 (95% CI=3.8-13.5) and four were non-responders with median liver scores of 2.5 (95% CI=1.2-4.3). Median liver scores for the three control cows were 1 (95% CI=-0.8-2.1). Activities of GGT increased in subclinical and clinical cows around Day 7. The milk yield of all cows treated with sporidesmin, including non-responder cows, started to decrease on Day 1, and reached a nadir (a drop of between 9 and 85%) on Day 7. CONCLUSIONS AND CLINICAL RELEVANCE It is likely that the overall effects of sporidesmin consumption on milk production by the national herd in New Zealand are hugely underestimated, especially considering its effects on non-responder and subclinical cows as shown in this trial. In view of the results presented here, the authors are suggesting a change to the definition of response to sporidesmin from non-responder, subclinical, and clinical, to subclinical-low, subclinical-high, and clinical, when measuring a combination of GGT activities, clinical signs and milk yields during facial eczema-risk seasons (summer-autumn).

Reactions of nitric oxide on Rh6+ clusters: abundant chemistry and evidence of structural isomers.

We report the first results of a new instrument for the study of the reactions of naked metal cluster ions using techniques developed by Professor Bondybey to whom this issue is dedicated. Rh6+ ions have been produced using a laser vaporization source and injected into a 3 T Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer where they are exposed to a low pressure (< 10(-8) mbar) of nitric oxide, NO. This system exhibits abundant chemistry, the first stages of which we interpret as involving the dissociative chemisorption of multiple NO molecules, followed by the liberation of molecular nitrogen. This yields key intermediates such as [Rh6O2]+ and [Rh6O4]+. The formation of the latter, after adsorption of four NO molecules, marks a change in the chemistry observed with further NO molecules adsorbed (presumably molecularly) without further N2 evolution until saturation is apparently reached with the [Rh6O4(NO)7]+ species. We analyse the data in terms of a simple 12-stage reaction mechanism, and we report the relative rate constants for each step. The trends in reactivity are assessed in terms of conceivable structures and the results are discussed where appropriate by comparison with extended surface studies of the same system. Particular attention is paid to the first step in the reaction (Rh6(+) + NO --> [Rh6NO]+) which exhibits distinctly bi-exponential kinetics, an observation we interpret as evidence for two different structural isomers of the Rh6+ cluster with one reacting more than an order of magnitude faster than the other.

Parameterising matrix-assisted laser desorption/ionization (MALDI): effect of solvents and co-additives on analyte peak intensities.

The peak intensities obtained when 2,5-dihydroxybenzoic acid (DHB) was used as a 'classic' matrix were measured using substance P (SP) and betacyclodextrin (BCD) as analytes. Enhancements in peak intensities were observed going from 1:1 MeOH/H2O to dimethylforamide (DMF) as matrix solvents. Also non-covalent interactions between SP and solvent and DHB were observed suggesting close interactions between matrix, solvent and analyte in the gas-phase. Peak enhancements were previously reported with 'superDHB' (DHB and 2-hydroxy-5-methoxybenzoic acid at 10% v/v). Co-addition of structural analogues and their respective absorption coefficients were determined. It was found that other analogues used as co-matrices could give analyte peak enhancement similar to reported for sDHB with the additional benefit that some analogues could act as matrices with DHB addition. No direct correlation was observed between absorption coefficient and the ability of the molecule to act as a 'good' UV MALDI matrix.

Protein-ligand and protein-protein interactions studied by electrospray ionization and mass spectrometry.

Electrospray ionization has made possible the transference of non-covalently bound complexes from solution phase to high vacuum. In the process, a complex acquires a net charge and becomes amenable to measurement by MS. FTICR (Fourier-transform ion cyclotron resonance) MS allows these ions to be measured with sufficiently high resolution for the isotopomers of complexes of small proteins to be resolved from each other (true for complexes up to about 100 kDa for the most powerful FTICR instruments), which is of crucial significance in the interpretation of spectra. Results are presented for members of the S100 family of proteins, demonstrating how non-covalently bound complexes can be distinguished unambiguously from covalently bound species. Consideration relevant both to determination of binding constants in solution from the gas-phase results and to the elucidation of protein folding and unfolding in solution are discussed. The caveats inherent to the basic approach of using electrospray and MS to characterize protein complexes are weighed and evaluated.

Supramolecular organization of alpha,alpha'-disubstituted sexithiophenes.

The self-assembly of alpha,alpha'-linked sexithiophenes with chiral and achiral penta(ethylene glycol) chains attached at the alpha-positions of the terminal rings, that is, 2,2':5',2'':5'',2''':5''',2'''':5'''',2'''''-sexithiophene-5,5'''''-dicarboxylic acid-2S)-2-methyl-3,6,9,12,15-pentaoxahexadecyl ester (1) and 2,2':5',2'':5'',2''':5'''',2''''':5''''',2'''''-sexithiophene-5,5'''''-dicarboxylic acid-3,6,9,12,15-pentaoxahexadecyl ester (2), respectively is described. Analysis of the UV/vis, fluorescence, circular dichroism, and circular polarization of luminescence spectroscopic data shows that these compounds form chiral aggregates in polar solvents and in the solid state. In n-butanol aggregation occurs at temperatures below 30 degrees C, while above this threshold temperature the aggregates break up without an intermediate disordered state of aggregation, and the compounds are molecularly dissolved. The "melting temperature" of the aggregates depends on the concentration of sexithiophene, indicating that the optical changes observed are a result of intermolecular processes. Mass spectrometric measurements reveal that 1 and 2 can form mixed aggregates. Analysis of the optical spectra reveals that in these mixed aggregates, chiral 1 molecules act as "sergeants" to direct the packing of the "soldiers" 2, illustrating cooperativity within the columns. In water, the same type of chiral aggregates are formed as in n-butanol below 30 degrees C; however, these aggregates are still present, but the chirality is lost above 30 degrees C. In spin-coated films of 1 chiral aggregates are present. AFM studies show that 1 self-organizes into chiral fiberlike structures in the solid state. Furthermore both 1 and 2 display thermotropic liquid crystalline behavior between 180 and 200 degrees C.

Repair of oxidized proteins. Identification of a new methionine sulfoxide reductase.

Oxidation of methionine residues to methionine sulfoxide can lead to inactivation of proteins. Methionine sulfoxide reductase (MsrA) has been known for a long time, and its repairing function well characterized. Here we identify a new methionine sulfoxide reductase, which we referred to as MsrB, the gene of which is present in genomes of eubacteria, archaebacteria, and eucaryotes. The msrA and msrB genes exhibit no sequence similarity and, in some genomes, are fused. The Escherichia coli MsrB protein (currently predicted to be encoded by an open reading frame of unknown function named yeaA) was used for genetic, enzymatic, and mass spectrometric investigations. Our in vivo study revealed that msrB is required for cadmium resistance of E. coli, a carcinogenic compound that induces oxidative stress. Our in vitro studies, showed that (i) MsrB and MsrA enzymes reduce free methionine sulfoxide with turn-over rates of 0.6 min(-1) and 20 min(-1), respectively, (ii) MsrA and MsrB act on oxidized calmodulin, each by repairing four to six of the eight methionine sulfoxide residues initially present, and (iii) simultaneous action of both MsrA and MsrB allowed full reduction of oxidized calmodulin. A possibility is that these two ubiquitous methionine sulfoxide reductases exhibit different substrate specificity.

Specific electrochemical nitration of horse heart myoglobin.

Earlier findings on electronitration of hen egg-white lysozyme demonstrated a product which was mononitrated at Tyr23, by ion-exchange chromatography, absorbance at 430 nm, dithionite reduction, and Edman sequencing of a nitrated proteolytic peptide. However, the whole protein was not sequenced; therefore, although the enzyme remained active upon nitration, reaction at other residues could not be completely eliminated. This study has now been extended to the redox protein myoglobin. We demonstrate the novel electronitration (electrooxidation in the presence of nitrite) of a specific tyrosine residue in horse heart myoglobin and also in apomyoglobin. Production of the yellow chromophore, 3-nitrotyrosine (3-NT), was apparent in apomyoglobin from A430 but was masked in holomyoglobin by the Soret band. In both cases, the presence of 3-NT in the electronitrated samples was further indicated by the binding of antibody to 3-NT in Western blots. High-resolution electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FTICR) mass spectrometry revealed a reaction product at [M + 45] (consistent with substitution of NO2 for H), indicating that the nitration reaction is the only reaction occurring which gives rise to a change in mass in the electrooxidation. Fragmentation mass spectrometry identified the nitration site as Tyr103, with no nitration at Tyr146. The procedure may be useful in preparing model nitrated proteins for the study of disease mechanisms.

The dimerization interface of the metastasis-associated protein S100A4 (Mts1): in vivo and in vitro studies.

The S100 calcium-binding proteins are implicated in signal transduction, motility, and cytoskeletal dynamics. The three-dimensional structure of several S100 proteins revealed that the proteins form non-covalent dimers. However, the mechanism of the S100 dimerization is still obscure. In this study we characterized the dimerization of S100A4 (also named Mts1) in vitro and in vivo. Analytical ultracentrifugation revealed that apoS100A4 was present in solution as a mixture of monomers and dimers in a rapidly reversible equilibrium (K(d) = 4 +/- 2 microm). The binding of calcium promoted dimerization. Replacement of Tyr-75 by Phe resulted in the stabilization of the dimer. Helix IV is known to form the major part of the dimerization interface in homologous S100 proteins. By using the yeast two-hybrid system we showed that only a few residues of helix IV, namely Phe-72, Tyr-75, Phe-78, and Leu-79, are essential for dimerization in vivo. A homology model demonstrated that these residues form a hydrophobic cluster on helix IV. Their role is to stabilize the structure of individual subunits rather than provide specific interactions across the dimerization surface. Our mutation data showed that the specificity at the dimerization surface is not particularly stringent, which is consistent with recent data indicating that S100 proteins can form heterodimers.

Heterocomplex formation between metastasis-related protein S100A4 (Mts1) and S100A1 as revealed by the yeast two-hybrid system.

S100A4 (Mts1) is a Ca(2+)-binding protein of the S100 family. This protein plays an important role in promoting tumor metastasis. In order to identify S100A4 interacting proteins, we have applied the yeast two-hybrid system as an in vivo approach. By screening a mouse mammary adenocarcinoma library, we have demonstrated that S100A4 forms a heterocomplex with S100A1, another member of the S100 family. The non-covalent heterodimerization was confirmed by fluorescence spectroscopy and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Mutational analysis revealed that replacement of Cys(76) and/or Cys(81) of S100A4 by Ser abolishes the S100A4/S100A1 heterodimerization, but does not affect the S100A4 homodimerization in vivo.

Calmodulin-peptide interactions: apocalmodulin binding to the myosin light chain kinase target-site.

Noncovalent binding of the synthetic peptide RS20 to calmodulin in the presence of calcium was confirmed by electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry to form a complex with a 1:1:4 calmodulin/RS20/calcium stoichiometry. There was no evidence for formation of a calmodulin-RS20-Ca(2) species. The absence of calmodulin-RS20-Ca(2) would be consistent with models in which the two globular domains are coupled functionally. There was evidence that calmodulin, RS20-calmodulin without associated calcium, and calmodulin-RS20-Ca(4) existed together in solution, whereas calmodulin-calcium complexes were absent. It is proposed that calcium binding to form the calmodulin-RS20-Ca(4) complex occurs after an initial RS20-calmodulin binding event, and serves to secure the target within the calmodulin structure. The binding of more than one RS20 molecule to calmodulin was observed to induce unfolding of calmodulin.

A novel Ca2+ binding protein associated with caldesmon in Ca2+-regulated smooth muscle thin filaments: evidence for a structurally altered form of calmodulin.

Smooth muscle thin filaments are made up of actin, tropomyosin, the inhibitory protein caldesmon and a Ca2+-binding protein. Thin filament activation of myosin MgATPase is Ca2+-regulated but thin filaments assembled from smooth muscle actin, tropomyosin and caldesmon plus brain or aorta calmodulin are not Ca2+-regulated at 25 degrees C/50 mM KCl. We isolated the Ca2+-binding protein (CaBP) from smooth muscle thin filaments by DEAE fast-flow chromatography in 6 M urea and phenyl sepharose chromatography using sheep aorta as our starting material. CaBP combines with smooth muscle actin, tropomyosin and caldesmon to reconstitute a normally regulated thin filament at 25 degrees C/50 mM KCl. It reverses caldesmon inhibition at pCa5 under conditions where CaM is largely inactive, it binds to caldesmon when complexed with actin and tropomyosin rather than displacing it and it binds to caldesmon independently of [Ca2+]. Amino acid sequencing, and electrospray mass spectrometry show the CaBP is identical to CaM. Structural probes indicate it is different: calmodulin increases caldesmon tryptophan fluorescence but CaBP does not. The distribution of charged species in electrospray mass spectrometry and nozzle skimmer fragmentation patterns are different indicating a less stable N-terminal lobe for CaBP. Brief heating abolishes these special properties of the CaBP. Mass spectrometry in aqueous buffer showed no evidence for the presence of any covalent or non-covalently bound adduct. The only remaining conclusion is that CaBP is calmodulin locked in a metastable altered state.

Evidence of noncovalent dimerization of calmodulin.

Calcium-binding proteins, such as S-100, dimerize readily, and this phenomenon plays an important role in their regulation of target enzymes [Krebs, J., Quadroni, M. & Van Eldik, L.J. (1995) Nat. Struct. Biol. 2, 711-714; Kilby, P.M., Van Eldik, L.J. & Roberts, G. C. (1996) Structure 4, 1041-1052]. We have investigated by Fourier-transform ion cyclotron resonance (FTICR) MS the conformational states of the calcium-binding protein calmodulin, and present clear evidence for a calmodulin dimer formed as a result of noncovalent interactions between folded monomers. Ultra-high-resolution electrospray ionization (ESI) mass spectra for calmodulin, obtained with a 9.4 T FTICR mass spectrometer, are presented. With the use of denaturing solutions (1 : 1 acetonitrile/water + 1% formic acid), relatively high charge states (20 < z < 10) of monomeric calmodulin ions were detected, whereas when calmodulin was electrosprayed from buffer, monomers ions with only 5-10 charges were detected. CD measurements for calmodulin in buffered solution revealed that its alpha-helical content was significantly higher than that for calmodulin in acetonitrile/water solutions, consistent with a proposition that changes in charge state distributions observed in the MS experiments reflect differing states of calmodulin folding. Under buffered conditions, noncovalently bound calmodulin dimers were observed by ESI FTICR MS. Analytical ultracentrifugation experiments carried out in the same solution conditions as those used in the MS experiments were consistent with the proposed calmodulin dimer-monomer equilibrium. The ultra-high mass resolution achieved with the 9.4 T FTICR mass spectrometer allowed unequivocal identification of the noncovalent, as opposed to covalent, character of the calmodulin dimer.

Determination of end groups of synthetic polymers by matrix-assisted laser desorption/ionization: high-energy collision-induced dissociation.

Matrix-assisted laser desorption/ionization has been combined with high-energy collision-induced dissociation for the analysis of poly(ethylene glycols) with butanoyl, benzoyl and acetyl end groups, using novel technology comprising a magnetic-sector mass spectrometer and ion buncher with an in-line quadratic-field ion mirror. High-energy (>8 keV) collision-induced dissociation facilitated unambiguous end-group determination of these polymers, providing masses of end groups and structural information. The high-energy collision-induced dissociation also provided information regarding repeat units.

Analysis of nisin A and some of its variants using Fourier transform ion cyclotron resonance mass spectrometry.

The lantibiotic nisin and some of its variants and degradation products have been characterized, using a 9.4-T Fourier transform ion cyclotron resonance mass spectrometer and electrospray ionization. The abundances of all products in the sample (i.e., major component, variants, degradation products, and adducts) have been measured quantitatively. The mass resolution obtained in the electrospray ionisation mass spectra was approximately 100,000 over the measured range. The resulting mass accuracy, better than 0.7 ppm (or within 0.001 Da) allowed the molecular masses and in many cases chemical formulae of most components in the mixture to be identified unambiguously. Additionally, amino acid sequence information on nisin and a variant [nisin + 18 Da] was obtained using sustained off-resonance irradiation collisional activated decomposition (SORI-CAD) of mass-selected precursor ions. Even after introducing collision gas into the mass analyser for the SORI-CAD experiments, the mass accuracy in the fragment ion mass spectra was approximately 5 ppm. It was established that the [nisin + 18 Da] molecule, present as a minor component in the mixture, was a species formed predominantly via hydration of nisin at position 33, i.e., [Ser33]nisin, with a small contribution due to hydration at position 5,[2-hydroxy-Ala5]nisin.

Probing the effects of cone potential in the electrospray ion source: consequences for the determination of molecular weight distributions of synthetic polymers.

Shifts in the relative intensities of oligomer ions are found to accompany changes in the cone potential in the electrospray ion source, which introduce uncertainties into average molecular weight determinations for polymer distributions. Similar shifts with changes in cone potential have long been recognized in the multiple-charge distributions of proteins and other biomolecules. In the case of multiple-charge distributions of a single, or small number of, species there are no major consequences for calculation of molecular weight; however, mass distributions and the averages thereof, are of major concern with synthetic polymers and understanding the shifts in relative intensities becomes critically important. We report here an evaluation of the effects of cone potentials on the molecular weight distributions of synthetic polymers, which we compare with the effects on charge-state distributions of peptides. The effects of cone potential have been modeled mathematically, from which we conclude that cone potentials exert a focusing effect dependent on the mass-to-charge ratios of ions. It is largely this focusing effect that determines the dependence of oligomer ion intensities upon cone potential in the ESI mass spectra of polymers. The influence of cone potential on molecular weight determinations of polymers of varying polydispersities (P(o)) is compared and discussed. For polymers with low polydispersities (e.g., narrow molecular weight poly(ethyleneglycol) standards with P(o) < 1.5), the variation in molecular weight determinations tends to be small (typically <5%), whereas with synthetic polymers with polydispersities greater than 2, variations in cone potential can influence molecular weight determinations significantly (by 100% or even more).

Ultrahigh Mass Accuracy in Isotope-Selective Collision-Induced Dissociation Using Correlated Sweep Excitation and Sustained Off-Resonance Irradiation: A Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Case Study on the [M + 2H](2+) Ion of Bradykinin.

Using electrospray ionization with a 9.4 T Fourier transform mass spectrometer, fragment ion spectra were acquired for a single isotopomer of doubly protonated bradykinin (molecular mass, 1059.6 Da). Correlated sweep excitation methods were applied to mass-select the single isotopomer (m/z = 530.8). Sustained off-resonance irradiation was used to activate and fragment the ions. The accuracy (in terms of m/z) in detection of the fragment ions was on average 1.2 ppm, making the assignments unambiguous. The methods employed would be generally applicable to ions in the mass range of approximately 50 Da to 50 kDa.

Comparison of high- and low-energy collision-induced dissociation tandem mass spectrometry in the analysis of glycoalkaloids and their aglycons.

Four aglycons (tomatidine, demissidine, solanidine, and solasodine) and three glycoalkaloids (α-tomatine, α-chaconine, and α-solanine) have been analyzed by positive ion liquid secondary ion high-energy and low-energy collision-induced dissociation (CID) tandem mass Spectrometry, performed on a four-sector (EBEB) and a hybrid (EBQQ) instrument, respectively. Both high- and low-energy collision-induced dissociation mass spectra of [M+H](+) ions of these compounds provided structural information that aided the characterization of the different aglycons and of the carbohydrate sequence and linkage sites in the glycoalkaloids. Low-energy CID favors charge-driven fragmentation of the aglycon rings, whilst high-energy CID spectra are more complex and contain additional ions that appear to result from charge-remote fragmentations, multiple cleavages, or complex charge-driven rearrangements. With respect to the structural characterization of the carbohydrate part, low-energy CID fragmentations of sugar residues in the glycoalkaloids generate Y n (+) ions and some low intensity Z n (+) ions; the high-energy spectra also exhibit strong (1,5)X n (+) ions, formed by multiple cleavage of the sugar ring, and significant Z n (+) ions.

Analysis of glycoalkaloids from potato shoots and tomatoes by four-sector tandem mass spectrometry with scanning-array detection: comparison of positive ion and negative ion methods.

A wide range of glycoalkaloids from potato shoots and tomatoes, including trisaccharide-containing glycoalkaloids (alpha-chaconine, alpha-solanine, and alpha-solasonine), tetrasaccharide-containing glycoalkaloids (alpha-tomatine and demissine), and disaccharide-containing glycoalkaloids (beta 1-chaconine, beta 2-chaconine, and beta-solamargine), have been studied by both positive and negative ion liquid secondary ion and four-sector tandem mass spectrometry with scanning-array detection. In positive ion mode, collisionally induced dissociation tandem mass spectra of the [M + H]+ ions induce three major fragmentation processes, Z cleavage, Y cleavage, and 1,5X cleavage, which are structurally informative. Signals resulting from Z0, Y0, and 1,5X0 cleavages provide information on the nature of various aglycone moieties in all glycoalkaloids. Linkages and positions of the sugars in trisaccharide- and tetrasaccharide-containing glycoalkaloids are indicated by the presence or absence of the ions corresponding to Z alpha/beta and Y alpha/beta cleavages and intensity differences of the peaks due to 1,5X alpha and 1,5X beta cleavages, respectively. In negative ion mode, collisionally induced dissociation tandem mass spectra of the [M - H]- ions induce Y cleavage as the major fragmentation process. The location of the terminal sugars in branched trisaccharide and tetrasaccharide glycoalkaloids is indicated by the difference in intensity of the ions due to Y alpha cleavage and Y beta cleavage. Isomeric structures cannot, however, be differentiated unambiguously; complete structural assignment is only possible by NMR of purified components. Both positive and negative ion tandem mass spectrometry are considered to be suitable for the characterisation of glycoalkaloids in mixtures. The positive ion method has the advantage of (i) a lower detection limit than in conventional mass spectrometry; (ii) numerous and intense fragment ions which are structurally informative; and (iii) the capability of analyzing minor components in crude extracts. Comparable analysis by other analytical means would not have provided the amount of structural information on the components in the glycoalkaloid mixtures.