Biomedical subjects

P S Belton

Publications and source records attributed to P S Belton.

At least 19 recordsLinked to original sources

PubMed2006

Alteration of kafirin and kafirin film structure by heating with microwave energy and tannin complexation.

Heating with microwave energy and tannin complexation of kafirin both increase the tensile strength of cast kafirin bioplastic films. The effects of these treatments on the molecular structure of kafirin and of kafirin in the film were investigated. SDS-PAGE of heated wet kafirin showed an increase in kafirin oligomers. Disulfide groups increased in heated kafirin and in films made from the heated kafirin. Fourier transform infrared (FTIR) spectroscopy of heated kafirin and films made from the heated kafirin indicated an increase in beta-sheet conformation. In contrast, kafirin complexation with tannic acid (TA) and sorghum condensed tannin (SCT) resulted in a slight decrease in beta-sheet conformation in the kafirin and a larger decrease in the kafirin in the films. Raman spectroscopy showed that, with TA, there was a shift in peak from 1710 to 1728 cm(-1) for kafirin-tannic acid complexes, indicating kafirin and tannic acid interaction. The protein conformational changes presumably facilitated cross-linking between kafirin molecules and/or between kafirin and the tannins. Thus, although both heating with microwave energy and tannin complexation cause cross-linking of kafirin to increase film tensile strength, their effects on kafirin structure appear to be different.

Electrophoresis, Polyacrylamide Gel↗

PubMed2003

Molecular structures and interactions of repetitive peptides based on wheat glutenin subunits depend on chain length.

Synthetic and recombinant peptide models of the central repetitive domain of the high molecular weight subunits of wheat glutenin with different numbers of the consensus repeat motifs PGQGQQ + GYYPTSLQQ (21, 45, 110, and 203 residues long) and a recombinant 58,000-Da relative molecular mass (M(r) 58,000) repetitive peptide from a single subunit (1Dx5) are studied using Fourier transform IR spectroscopy. The spectra of the dry peptides are very similar; at low water contents (<76% relative humidity) there is an increase in beta-sheet structures in all peptides. However, on further hydration the content of beta sheets decrease and more beta turns are observed. The changes during the second step of hydration are very marked in the 21 and 45 residue peptides, but they are less apparent in the longer perfect repeat peptides. In the 110 and 203 residue peptides hydration results in increased contents of intermolecular beta-sheets and less beta-turn formation. In contrast, the beta-turn content of the M(r) 58,000 peptide increases during the second hydration step. The decreased extent of structure changes with increasing chain length indicates that cumulative intermolecular interactions, in particular hydrogen bonds, are an important factor in determining the structures in the solid state. The regularity of the perfect repeat sequences in the 21, 45, 110, and 203 residue peptides may favor the formation of larger stretches of intermolecular beta sheets. In contrast, the M(r) 58,000 peptide contains imperfect repeats (in common with native glutenin subunits), which may limit its ability to form intermolecular beta sheets.

Amino Acid Sequence↗

PubMed2002

Sequence and properties of HMW subunit 1Bx20 from pasta wheat (Triticum durum) which is associated with poor end use properties.

The gene encoding high-molecular-weight (HMW) subunit 1Bx20 was isolated from durum wheat cv. Lira. It encodes a mature protein of 774 amino acid residues with an M(r) of 83,913. Comparison with the sequence of subunit 1Bx7 showed over 96% identity, the main difference being the substitution of two cysteine residues in the N-terminal domain of subunit 1Bx7 with tyrosine residues in 1Bx20. Comparison of the structures and stabilities of the two subunits purified from wheat using Fourier-transform infra-red and circular dichroism spectroscopy showed no significant differences. However, incorporation of subunit 1Bx7 into a base flour gave increased dough strength and stability measured by Mixograph analysis, while incorporation of subunit 1Bx20 resulted in small positive or negative effects on the parameters measured. It is concluded that the different effects of the two subunits could relate to the differences in their cysteine contents, thereby affecting the cross-linking and hence properties of the glutenin polymers.

Amino Acid Sequence↗

PubMed2002

Interaction between protein allergens and model gastric emulsions.

The observed resistance to pepsinolysis of known food allergens has been suggested as a predictor of their allergenic risk. Consequently, resistance to pepsinolysis has become incorporated into decision tree assessment for potential allergenic risk posed by novel foods. However, existing methods take little account of the interaction between food structure and physiological conditions existing during digestion in vivo. Here we show that a range of protein allergens can adsorb to model stomach emulsions, providing a further means of resisting digestion. We also show that raising the pH and the addition of bile salts to a model stomach emulsion, thereby mimicking the duodenal environment, has the effect of desorbing the adsorbed protein.

Adsorption↗

PubMed2002

Allergens of the cupin superfamily.

The cupin family comprises a family of proteins possessing a common beta-barrel structure that is thought to have originated in a prokaryotic ancestor. This structural motif is found as a single domain in fungal spherulins, fern sporulins and the germins/oxalate oxidase proteins of plants, while the globular storage proteins of plants, called legumins (11 S) and euvicilins (7 S), are two-domain cupins. The 11 S globulins are hexameric heteroligomeric proteins of M (r) approximately 360000, with each subunit comprising an acidic 30000-40000- M (r) polypeptide that is disulphide-linked to a 20000- M (r) basic polypeptide. A number of cupins have been identified as major plant food allergens, including the 7 S globulins of soybean (beta-conglycinin), peanut (conarachin; Ara h 1), walnut (Jug r 2) and lentil, and the 11 S globulins of peanut (arachin; Ara h 3), soybean (glycinin) and possibly also coconut and walnut. Other members of the cupin superfamily have not been identified as allergens, with the exception of one germin (germination-specific protein) from pepper. Cupins are generally very stable proteins. A summary of our current knowledge of allergenic seed storage globulins will be presented, together with an overview of cupin structure and stability properties, as illustrated by the allergenic soya globulins, glycinin and beta-conglycinin.

Allergens↗

PubMed2001

Solid state NMR and X-ray diffraction studies of alpha-D-galacturonic acid monohydrate.

Crystalline alpha-D-galacturonic acid monohydrate has been studied by 13C CPMAS NMR and X-ray crystallography. The molecular dynamics were investigated by evaluating 13C spin-lattice relaxation in the rotating frame (T1rho) and chemical-shift-anisotropy properties of each carbon. Only limited molecular motions can be detected in the low frequency (< 10(4) Hz) range by 13C relaxation time measurements (T1rho) and changes of chemical shift anisotropy properties as a function of temperature. X-ray analysis (at both ambient temperature and 150 K) shows that the acid has the usual chair-shaped, pyranose ring conformation, and that the acid and water molecules are linked, through all their O-H groups, in an extensively hydrogen-bonded lattice.

Carbohydrate Conformation↗

PubMed2001

Physicochemical studies of caroubin: a gluten-like protein.

It has been reported that caroubin, a protein mixture obtained from carob seeds, has rheological properties similar to those of gluten. Comparative studies of the effects of hydration and temperature on caroubin and gluten were carried out with the aid of NMR, FTIR, scanning electron microscopy, and differential scanning calorimetry techniques. The results show that caroubin has a more ordered structure than gluten and that hydration has little effect on its secondary structure when compared to gluten. Caroubin is more easily accessible to water than gluten, suggesting that caroubin is more hydrophilic in nature. On hydration, caroubin, like gluten, forms fibrillar structures and sheets.

Calorimetry, Differential Scanning↗

PubMed2000

Expression and characterisation of a highly repetitive peptide derived from a wheat seed storage protein.

The high molecular weight (HMW) subunit group of wheat seed storage proteins impart elasticity to wheat doughs and glutens. They consist of three domains: non-repetitive N- and C-terminal domains, which contain cysteine residues for covalent cross-linking, and a central domain consisting of repeated sequences. The circular dichroism and infrared (IR) spectra of an intact HMW subunit were compared with those of a peptide corresponding to the central repetitive domain expressed in Escherichia coli. This allowed the structure of the central domain to be studied in the absence of the N- and C-terminal domains and the contributions of these domains to the structure of the whole protein to be determined. In solution the peptide showed the presence of beta-turns and polyproline II-like structure. Variable temperature studies indicated an equilibrium between these two structures, the polyproline II conformation predominating at low temperatures and the beta-turn conformation at higher temperatures. IR in the hydrated solid state also indicated the presence of beta-turns and intermolecular beta-sheet structures. In contrast, spectroscopy of the whole subunit showed the presence of alpha-helix in the N- and C-terminal domains. The content of beta-sheet was also higher in the whole subunit, indicating that the N- and C-terminal domains may promote the formation of intermolecular beta-sheet structures between the repetitive sequences, perhaps by aligning the molecules to promote interaction.

Amino Acid Sequence↗

PubMed2000

Nuclear magnetic resonance studies of the hydration of proteins and DNA.

The behaviour of water in the presence of proteins and DNA as elucidated by nuclear magnetic resonance is reviewed. The picture that emerges is that in dilute solution only those water molecules in the interior of the biopolymers or in clefts have their motions substantially affected. In concentrated systems the situation is more complicated because many more motions have to be considered, but there is no evidence of special effects due to the biopolymers being present. The case of nonfreezing water in protein solutions is considered, and it is suggested that this is not evidence for 'bound' water but simply due to the effects of the inhibition of protein precipitation.

Biopolymers↗

PubMed2000

13C CPMAS studies of plant cell wall materials and model systems using proton relaxation-induced spectral editing techniques.

The solid state 13C CPMAS NMR spectra of plant cell walls are often complex owing to superposition of resonances from different polysaccharides and the heterogeneity of the cell wall assembly. In this paper, we describe the application of a set of proton relaxation-induced spectral editing (PRISE) experiments which combine 1H relaxation properties (T1, T1rho, T2) with 13C high resolution spectroscopy (CPMAS) to relate the dynamics of the plant cell walls and model systems to their domain structural details. With PRISE it has been found that in plant cell wall materials, cellulose is always associated with the long components of spin-lattice relaxation in both the laboratory and rotating frames whereas non-cellulose polysaccharides (pectin and hemicellulose) are associated with the short ones. For the proton T2 relaxation, cellulose is only associated with the short component (below 20 micros), pectin contributes to both the short component and the long one.

Carbon Isotopes↗

PubMed2000

Green tea polyphenols react with 1,1-diphenyl-2-picrylhydrazyl free radicals in the bilayer of liposomes: direct evidence from electron spin resonance studies.

Free radical scavenging reactions of green tea polyphenols (GTP) were investigated with electron spin resonance (ESR) spectroscopy in the phospholipid bilayer of liposomes, using 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical as a model. The results showed that (1) GTP reacts with DPPH radicals in the bilayer of liposomes of both 1-hexadecanoyl-2-[(cis,cis,cis,cis,cis,cis)-4,7,10, 13,16,19-docosahexaenoyl]-sn-glycero-3-phosphocholine (DHAPC) and 1, 2-di[cis-9-hexadecenoyl]-sn-glycero-3-phosphocholine) (DPPC); and (2) GTP protects DHAPC liposomes effectively from the oxidation initiated by DPPH radicals. These results provide direct evidence that GTP reacts with free radicals in the model membrane and support the hypothesis that GTP protects unsaturated phospholipids from oxidation by reacting directly with the radicals.

Bepridil↗

PubMed1999

Proton NMR relaxation studies of solid tyrosine derivatives and their mixtures with L-leucinamide.

Proton NMR relaxation time measurements were carried out on solid tyrosine derivatives: acetyl-L-tyrosine ethyl ester (Ac-Tyroet), N-carbobenzyloxy-L-tyrosine ethyl ester (CBZ-Tyroet), N-trifluoroacetyl-L-tyrosine ethyl ester (TFAc-Tyroet) and their mixtures with L-leucinamide. It was found that spin-lattice relaxation was driven mainly by methyl group rotation it low temperature for the pure solids and the mixtures. Benzene ring flipping motion and a third motion (possibly whole molecule tumbling) were found to be responsible for relaxing Ac-Tyroet and CBZ-Tyroet at high temperature. However, these motions were highly hindered in TFAc-Tyroet. Molecular tumbling motion was detected in the supercooled liquid mixtures of L-leuNH/CBZ-Tyroet and L-leuNH/Ac-Tyroet, while this motion is absent in the mixture L-leuNH/TFAc-Tyroet. The hindered motion in TFAc-Tyroet may be one of the factors affecting its ability to form a supercooled liquid with L-leucinamide.

Benzene↗

PubMed1999

13C MAS NMR studies of the effects of hydration on the cell walls of potatoes and Chinese water chestnuts.

13C NMR with magic angle spinning (MAS) has been employed to investigate the cell walls of potatoes and Chinese water chestnuts over a range of hydration levels. Both single-pulse excitation (SPEMAS) and cross-polarization (CPMAS) experiments were carried out. Hydration led to a substantial increase in signal intensities of galactan and galacturonan in the SPEMAS spectra and a decrease in line width, implying mobilization in the backbone and side chains of pectin. In CPMAS spectra of both samples, noncellulose components showed signal loss as hydration increased. However, the signals of some galacturonan in the 3(1) helix configuration remained in the spectra even when the water content was as high as 110%. Cellulose was unaffected. It is concluded that the pectic polysaccharides experience a distribution of molecular conformations and mobility, whereas cellulose remained as typical rigid solid.

Cell Wall↗

PubMed1999

Selected spin probes for the electron spin resonance study of the dynamics of water and lipids in doughs.

New water-soluble and lipid-soluble spin probes suitable for the ESR investigation of the physical states and interactions of components of dough have been developed. This paper reports some preliminary findings on the suitability of these probes for this type of investigation. Rotational correlation times have been measured for the spin probes in water, dough, oil, and a starch/water mixture. An increase in rotational correlation time of the spin probe corresponds to an increase in microviscosity of the medium. Changes observed in correlation times of the water-soluble spin probes in doughs and in water/starch mixtures clearly correspond to a gelatinization process when the mixtures are heated above 60 degrees C. These irreversible changes, clearly important in the baking process, were monitored by following the change of mobility of a spin probe in doughs over a wide temperature range. The similarity of the results from the two sets of experiments suggests that the phenomenon of the increase of correlation times with temperature in doughs is attributable to the starch component. The lipid-soluble spin probe was found to be located preferentially in the lipid phase of the dough.

Electron Spin Resonance Spectroscopy↗

PubMed1998

Molecular motions of D-alpha-galacturonic acid (GA) and methyl-D-alpha-galacturonic acid methyl ester (MGAM) in the solid state-A proton NMR study.

The molecular motions of D-alpha-galacturonic acid monohydrate (GA) and its derivative methyl-alpha-D-galacturonic acid methyl ester monohydrate (MGAM) in the solid state have been studied using 1H NMR. Both protonated and deuterium exchanged samples have been used. Spin-lattice relaxation times in the laboratory and rotating frames as well as second moments have been measured over the temperature range 90-370 K. Analysis of results has shown that in GA spin-lattice relaxation is chiefly by hydroxyl groups and water of crystallization. In MGAM, methyl groups dominate spin-lattice relaxation in the laboratory frame at the low temperature. Hydroxyl groups and water of crystallization contribute to the spin-lattice relaxation in the laboratory frame in the high temperature region. In the rotating frame motion of hydroxyl groups and water of crystallization provide the main relaxation pathway. Changes in the static second moment with temperature can be reasonably well predicted using values of correlation time and motionally averaged second moments obtained by fitting the spin-lattice relaxation data. 13C CPMAS spectra for GA and MGAM are also described.

Carbon Isotopes↗

PubMed1997

NMR and the mobility of water in polysaccharide gels.

An analysis of the possible modes of motion of water molecules in polysaccharide gels indicates that the interpretation of NMR results does not require the supposition of a class of 'bound water' with highly perturbed motional states. There may, however, be water molecules associated with junction zones in the gels whose motions are restricted either by incorporation into the molecular secondary structure or as interstitial water in crystallites. Hydration and dehydration effects as well as the phenomenon of non-freezing water may all be explained within a framework of well understood processes. It is concluded that there is no requirement to appeal to 'bound water' to explain any of the properties of water in polysaccharide gels.

Gels↗

PubMed1996

Fourier transform IR spectroscopic study of hydration-induced structure changes in the solid state of omega-gliadins.

The hydration of omega-gliadins and party deamidated and esterified omega-gliadins has been studied by Fourier transform IR spectroscopy. The secondary structure of the fully hydrated proteins was a mixture of beta-turns and extended chains, with a small amount of intermolecular beta-sheets. The absorption of the glutamine side chain amide groups contributed considerably to the amide I band with two well-defined peaks at 1658 and 1610 cm-1. the amide I band of the dry native sample could not be resolved into single component bands. There the backbone structure seemed to be distorted by extensive hydrogen bonding involving glutamine side chains. With increasing water content, these hydrogen bonds were broken successively by water molecules, resulting in an increase in extended, hydrated structures, which gave rise to the formation of intermolecular beta-sheet structures. Above 35% (w/w) water the beta-sheet content fell sharply and was replaced by extensively hydrated extended structures. An amide I band similar to dissolved poly-L-proline proved that parts of the polymer were in a solution-like state. The replacement of many glutamine side chains in the esterified protein produced more resolved secondary structures even in the dry sample. The beta-sheet content of the dry sample was higher than in the native omega-gliadins, but hydration generally caused very similar changes. At all hydration levels the spectra indicated a more ordered structure than in the native sample. Overall, the modification caused changes that go beyond the simple presence or absence of glutamine bands.

Gliadin↗

PubMed1995

FTIR and NMR studies on the hydration of a high-M(r) subunit of glutenin.

The hydration behaviour of a purified high-M(r) subunit of glutenin has been studied using Fourier transform infra-red (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. The water-insoluble protein was examined in an unalkylated form with intermolecular disulfide bonds, and in a reduced and alkylated (unpolymerized) form. Hydration produced a marked increase in chain mobility, especially above a threshold water content of about 37% w/w. NMR experiments also showed that some parts of the chain were held in a much less mobile state, even at higher water contents. Little difference could be seen between alkylated and unalkylated subunits, implying that NMR is sensitive to localized motions, but not to any restrictions imposed by disulfide bridges close to the chain ends. FTIR spectra of the protein films have shown that increasing hydration enables changes to occur in favour of a more extended and beta-sheet-type structure. The changes in secondary structure are very noticeable at water contents corresponding to the NMR mobility threshold. The behaviour is influenced by intermolecular interactions. beta-sheet formation is enhanced by the presence of disulfide bonds in the unalkylated samples. There is little evidence of beta-structure (sheet or extended chain) either in the dry state, where protein-protein interactions are strongest, or in dilute acetic acid solution, where the interactions are weakest. The balance between protein-protein and protein-water hydrogen-bonding interactions therefore appears to influence the formation of beta-sheet and extended chain structures, and these may in turn affect the elasticity of high M(r) subunits.

Alkylation↗