Carl Holt - Academia.edu (original) (raw)
Papers by Carl Holt
International Journal of Food Science and Technology, 1999
The physico-chemical properties are reported for a group of whey protein powders prepared on a co... more The physico-chemical properties are reported for a group of whey protein powders prepared on a commercial or serm-commercial scale by three companies and chemically characterized as described elsewhere (Holt et al., 1999). The dependence of the apparent p-lactoglobulin % on the recovered % showed that the nine samples could be placed in three distinct groups with p-lactoglobulin weight % of 70.9 ±1.1 (Group 1), 62.0 ± 3.4 (Group 2) and 39 5 ± 4.9 (Group 3). Measurements by 'H-NMR spectroscopy, on 3 of the samples confirmed that the native fold still predominated in the p-lactoglobulin. p-lactoglobulin could be crystallized from all the powders and the normal space group and cell dirnensions were determined for the 8 samples that gave crystals of good enough quality for X-ray studies. Differential scanning microcalorimetry of samples dispersed in a phosphate buffer showed a clear difference between Goups l and 2 with a more prominent peak due to a-lactalbumin in the Group 2 samples. Light scattering and size exclusion chromatography showed that two types of aggregates were present to a variable extent in all the samples and after a heat treatment, the larger aggregates tended to predommate in Correspondent Fax +44-1292-674184, e-mail holtc@hn san ac uk
Le Journal de Physique Colloques, 1986
Journal of Dairy Science, 2004
β-Lactoglobulin (β-LG) is the major whey protein of ruminant species and is also present in the m... more β-Lactoglobulin (β-LG) is the major whey protein of ruminant species and is also present in the milks of many, but not all, other species. Its amino-acid sequence and 3-dimensional structure show that it is a lipocalin, a widely diverse family, most of which bind small hydrophobic ligands and thus may act as specific transporters, as does serum retinol binding protein.
Biochemical Society transactions, 1995
Journal of dairy science, 2013
A typical casein micelle contains thousands of casein molecules, most of which form thermodynamic... more A typical casein micelle contains thousands of casein molecules, most of which form thermodynamically stable complexes with nanoclusters of amorphous calcium phosphate. Like many other unfolded proteins, caseins have an actual or potential tendency to assemble into toxic amyloid fibrils, particularly at the high concentrations found in milk. Fibrils do not form in milk because an alternative aggregation pathway is followed that results in formation of the casein micelle. As a result of forming micelles, nutritious milk can be secreted and stored without causing either pathological calcification or amyloidosis of the mother's mammary tissue. The ability to sequester nanoclusters of amorphous calcium phosphate in a stable complex is not unique to caseins. It has been demonstrated using a number of noncasein secreted phosphoproteins and may be of general physiological importance in preventing calcification of other biofluids and soft tissues. Thus, competent noncasein phosphoprotei...
Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1999
Casein micelles become mutually attractive when an exocellular polysaccharide produced by Lactoco... more Casein micelles become mutually attractive when an exocellular polysaccharide produced by Lactococcus lactis subsp. cremoris NIZO B40 (hereafter called EPS) is added to skim milk. The attraction can be explained as a depletion interaction between the casein micelles induced by the nonadsorbing EPS. We used three scattering techniques (small-angle neutron scattering, turbidity measurements, and dynamic light scattering) to measure the attraction. In order to connect the theory of depletion interaction with experiment, we calculated structure factors of hard spheres interacting by a depletion pair potential. Theoretical predictions and all the experiments showed that casein micelles became more attractive upon increasing the EPS concentration.
The Biochemical journal, Jan 15, 1997
Previous CD measurements of changes in the conformation of beta-lactoglobulin at neutral pH as a ... more Previous CD measurements of changes in the conformation of beta-lactoglobulin at neutral pH as a function of temperature indicated the formation of a molten globule state above approx. 70 degrees C. New CD measurements are reported at temperatures up to 80 degrees C with an instrument on the Daresbury synchrotron radiation source which gives spectra of good signal-to-noise ratio down to 170 nm. IR spectra were recorded up to 94.8 degrees C with a ZnSe circle cell and a single simplified model of the substructure of the amide I' band was used to give the fractional contents of beta-sheet structure unambiguously and independently of the CD spectroscopy. The results of both techniques, however, were in agreement in showing a progressive loss of beta-sheet structure with increasing temperature, beginning below the denaturation temperature. Nevertheless, the CD spectroscopy showed a fairly abrupt loss of virtually all the helical conformation at approx. 65 degrees C. Comparison of th...
The Biochemical journal, Jan 15, 1996
The ability of casein in the form of colloidal-sized casein micelles to modulate the phase separa... more The ability of casein in the form of colloidal-sized casein micelles to modulate the phase separation of calcium phosphate during milk secretion is adapted to produce nanometre-sized particles of calcium phosphate stabilized by a casein phosphopeptide (nanoclusters). The nanoclusters were prepared from an undersaturated solution of salts and the peptide by raising the pH homogeneously from about 5.5 to 6.7 with urea plus urease. Chemical analysis and IR spectroscopy showed that they comprise an amorphous dicalcium phosophate bound to the phosphopeptide. Multinuclear NMR spectroscopy of the cluster solutions showed that the small ions and free peptide in the solution were in a state of dynamic exchange with the nanoclusters. The peptide is linked to the calcium phosphate through its sequence of phosphorylated residues, but, in a proportion of adsorbed conformational states, the termini retain the conformational freedom of the unbound peptide. The ability of casein to form nanocluster...
Journal of dairy science, 1993
A brief overview is given of the methods of determining and predicting secondary structure in pro... more A brief overview is given of the methods of determining and predicting secondary structure in proteins. The secondary structures of the milk serum proteins, lactoferrin, alpha-lactalbumin, lysozyme, and beta-lactoglobulin, as determined by x-ray crystallography, are compared with the results of a joint prediction method. This comparison evaluates critically the degree of success achieved and helps define what can reasonably be expected from a prediction in the absence of a known structure. The value of supplementary information from spectroscopic methods and the use of templates and sequence information from related proteins in improving the confidence of predictions are illustrated. One point that emerges is the general overprediction of helix content by the joint prediction method such that, for an all-beta protein such as beta-lactoglobulin, the method of Garnier, Osguthorpe, and Robson, applied with the correctly selected decision constants, provides a somewhat better approach. ...
Applied and environmental microbiology, 1995
Infrared spectra of type cultures of the six recognized species of the genus Listeria and of List... more Infrared spectra of type cultures of the six recognized species of the genus Listeria and of Listeria grayi subsp. murrayi were recorded. By use of a library of 59 spectra, comprising at least six replicates of each type, discrimination by canonical variate analysis of the spectral amplitudes allowed all of the spectra to be correctly classified.
... in Milk Diffusate and Comparison with Experiment' CARL HOLT, DOUGLAS G. DALGLEISH, AND R... more ... in Milk Diffusate and Comparison with Experiment' CARL HOLT, DOUGLAS G. DALGLEISH, AND ROBERT JENNESS* Hannah ... magnesium is complexed to citrate as CaCit and MgCit, respectively, 162 HOLT, DALGLEISH, AND ... van Kreveld, A., and van Minnen, G. (1955) Neth. ...
International Journal of Food Science and Technology, 1999
The physico-chemical properties are reported for a group of whey protein powders prepared on a co... more The physico-chemical properties are reported for a group of whey protein powders prepared on a commercial or serm-commercial scale by three companies and chemically characterized as described elsewhere (Holt et al., 1999). The dependence of the apparent p-lactoglobulin % on the recovered % showed that the nine samples could be placed in three distinct groups with p-lactoglobulin weight % of 70.9 ±1.1 (Group 1), 62.0 ± 3.4 (Group 2) and 39 5 ± 4.9 (Group 3). Measurements by 'H-NMR spectroscopy, on 3 of the samples confirmed that the native fold still predominated in the p-lactoglobulin. p-lactoglobulin could be crystallized from all the powders and the normal space group and cell dirnensions were determined for the 8 samples that gave crystals of good enough quality for X-ray studies. Differential scanning microcalorimetry of samples dispersed in a phosphate buffer showed a clear difference between Goups l and 2 with a more prominent peak due to a-lactalbumin in the Group 2 samples. Light scattering and size exclusion chromatography showed that two types of aggregates were present to a variable extent in all the samples and after a heat treatment, the larger aggregates tended to predommate in Correspondent Fax +44-1292-674184, e-mail holtc@hn san ac uk
Le Journal de Physique Colloques, 1986
Journal of Dairy Science, 2004
β-Lactoglobulin (β-LG) is the major whey protein of ruminant species and is also present in the m... more β-Lactoglobulin (β-LG) is the major whey protein of ruminant species and is also present in the milks of many, but not all, other species. Its amino-acid sequence and 3-dimensional structure show that it is a lipocalin, a widely diverse family, most of which bind small hydrophobic ligands and thus may act as specific transporters, as does serum retinol binding protein.
Biochemical Society transactions, 1995
Journal of dairy science, 2013
A typical casein micelle contains thousands of casein molecules, most of which form thermodynamic... more A typical casein micelle contains thousands of casein molecules, most of which form thermodynamically stable complexes with nanoclusters of amorphous calcium phosphate. Like many other unfolded proteins, caseins have an actual or potential tendency to assemble into toxic amyloid fibrils, particularly at the high concentrations found in milk. Fibrils do not form in milk because an alternative aggregation pathway is followed that results in formation of the casein micelle. As a result of forming micelles, nutritious milk can be secreted and stored without causing either pathological calcification or amyloidosis of the mother's mammary tissue. The ability to sequester nanoclusters of amorphous calcium phosphate in a stable complex is not unique to caseins. It has been demonstrated using a number of noncasein secreted phosphoproteins and may be of general physiological importance in preventing calcification of other biofluids and soft tissues. Thus, competent noncasein phosphoprotei...
Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1999
Casein micelles become mutually attractive when an exocellular polysaccharide produced by Lactoco... more Casein micelles become mutually attractive when an exocellular polysaccharide produced by Lactococcus lactis subsp. cremoris NIZO B40 (hereafter called EPS) is added to skim milk. The attraction can be explained as a depletion interaction between the casein micelles induced by the nonadsorbing EPS. We used three scattering techniques (small-angle neutron scattering, turbidity measurements, and dynamic light scattering) to measure the attraction. In order to connect the theory of depletion interaction with experiment, we calculated structure factors of hard spheres interacting by a depletion pair potential. Theoretical predictions and all the experiments showed that casein micelles became more attractive upon increasing the EPS concentration.
The Biochemical journal, Jan 15, 1997
Previous CD measurements of changes in the conformation of beta-lactoglobulin at neutral pH as a ... more Previous CD measurements of changes in the conformation of beta-lactoglobulin at neutral pH as a function of temperature indicated the formation of a molten globule state above approx. 70 degrees C. New CD measurements are reported at temperatures up to 80 degrees C with an instrument on the Daresbury synchrotron radiation source which gives spectra of good signal-to-noise ratio down to 170 nm. IR spectra were recorded up to 94.8 degrees C with a ZnSe circle cell and a single simplified model of the substructure of the amide I' band was used to give the fractional contents of beta-sheet structure unambiguously and independently of the CD spectroscopy. The results of both techniques, however, were in agreement in showing a progressive loss of beta-sheet structure with increasing temperature, beginning below the denaturation temperature. Nevertheless, the CD spectroscopy showed a fairly abrupt loss of virtually all the helical conformation at approx. 65 degrees C. Comparison of th...
The Biochemical journal, Jan 15, 1996
The ability of casein in the form of colloidal-sized casein micelles to modulate the phase separa... more The ability of casein in the form of colloidal-sized casein micelles to modulate the phase separation of calcium phosphate during milk secretion is adapted to produce nanometre-sized particles of calcium phosphate stabilized by a casein phosphopeptide (nanoclusters). The nanoclusters were prepared from an undersaturated solution of salts and the peptide by raising the pH homogeneously from about 5.5 to 6.7 with urea plus urease. Chemical analysis and IR spectroscopy showed that they comprise an amorphous dicalcium phosophate bound to the phosphopeptide. Multinuclear NMR spectroscopy of the cluster solutions showed that the small ions and free peptide in the solution were in a state of dynamic exchange with the nanoclusters. The peptide is linked to the calcium phosphate through its sequence of phosphorylated residues, but, in a proportion of adsorbed conformational states, the termini retain the conformational freedom of the unbound peptide. The ability of casein to form nanocluster...
Journal of dairy science, 1993
A brief overview is given of the methods of determining and predicting secondary structure in pro... more A brief overview is given of the methods of determining and predicting secondary structure in proteins. The secondary structures of the milk serum proteins, lactoferrin, alpha-lactalbumin, lysozyme, and beta-lactoglobulin, as determined by x-ray crystallography, are compared with the results of a joint prediction method. This comparison evaluates critically the degree of success achieved and helps define what can reasonably be expected from a prediction in the absence of a known structure. The value of supplementary information from spectroscopic methods and the use of templates and sequence information from related proteins in improving the confidence of predictions are illustrated. One point that emerges is the general overprediction of helix content by the joint prediction method such that, for an all-beta protein such as beta-lactoglobulin, the method of Garnier, Osguthorpe, and Robson, applied with the correctly selected decision constants, provides a somewhat better approach. ...
Applied and environmental microbiology, 1995
Infrared spectra of type cultures of the six recognized species of the genus Listeria and of List... more Infrared spectra of type cultures of the six recognized species of the genus Listeria and of Listeria grayi subsp. murrayi were recorded. By use of a library of 59 spectra, comprising at least six replicates of each type, discrimination by canonical variate analysis of the spectral amplitudes allowed all of the spectra to be correctly classified.
... in Milk Diffusate and Comparison with Experiment' CARL HOLT, DOUGLAS G. DALGLEISH, AND R... more ... in Milk Diffusate and Comparison with Experiment' CARL HOLT, DOUGLAS G. DALGLEISH, AND ROBERT JENNESS* Hannah ... magnesium is complexed to citrate as CaCit and MgCit, respectively, 162 HOLT, DALGLEISH, AND ... van Kreveld, A., and van Minnen, G. (1955) Neth. ...