Composition and ultrastructure of calcium phosphate-citrate complexes in bovine milk systems

McGann, T. C. A.; Buchheim, W.; Kearney, Robert D.; Richardson, Thomas

doi:10.1016/0304-4165(83)90383-5

Cited by 65 publications

(41 citation statements)

References 14 publications

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“…By microscopy, the micellar calcium phosphate appeared as several distinct regions of higher electron density (microgranules) with an estimated diameter of about 2.5 nm [11]. Using highresolution transmission electron microscopy and diffraction methods, Mc Gann et al [11] and Lyster et al [12] indicated an amorphous nature of the micellar calcium phosphate. Van Dijk [13] proposed a specific formula showing the bond between micellar calcium phosphate and caseins.…”

Section: Micellar Calcium Phosphatementioning

confidence: 99%

“…By calculation of the apparent solubility product, a structure more like that of dicalcium phosphate and a modified structure Ca(HPO 4 ) 0.7 (PO 4 ) 0.2 was proposed by Holt [9,10]. By microscopy, the micellar calcium phosphate appeared as several distinct regions of higher electron density (microgranules) with an estimated diameter of about 2.5 nm [11]. Using highresolution transmission electron microscopy and diffraction methods, Mc Gann et al [11] and Lyster et al [12] indicated an amorphous nature of the micellar calcium phosphate.…”

Section: Micellar Calcium Phosphatementioning

confidence: 99%

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The minerals of milk

2005

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-The salt of milk constitutes a small part of milk (8-9 g·L -1 ); this fraction contains calcium, magnesium, sodium and potassium for the main cations and inorganic phosphate, citrate and chloride for the main anions. In milk, these ions are more or less associated between themselves and with proteins. Depending on the type of ion, they are diffusible (cases of sodium, potassium and chloride) or partially associated with casein molecules (cases of calcium, magnesium, phosphate and citrate), to form large colloidal particles called casein micelles. Today, our knowledge and understanding concerning this fraction is relatively complete. In this review, the different models explaining (i) the nature and distribution of these minerals (especially calcium phosphate) in both fractions of milk and (ii) their behaviour in different physico-chemical conditions, are discussed. milk / minerals / salts / calcium / phosphate / casein micelle

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Section: Micellar Calcium Phosphatementioning

confidence: 99%

Section: Micellar Calcium Phosphatementioning

confidence: 99%

The minerals of milk

2005

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“…OCP has also been shown to hydrolyse into calcium-deficient apatites but it was shown that dehydration through a thermal treatment could cause a significant decrease in crystallite size (Neslon and McLean 1984). Both OCP (McGann et al 1983) and DCPD can be in vitro precursors of HA , Addadi et al 2012) but have only rarely been detected in mineralised tissue. They are, however, common in pathological calcifications such as dental calculi, urinary stones and chondrocalcinoses (Cheng 1991), formed at lower pH.…”

Section: Introductionmentioning

confidence: 99%

Structural studies of hydrated samples of amorphous calcium phosphate and phosphoprotein nanoclusters

et al. 2016

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There are abundant examples of nanoclusters and inorganic microcrystals in biology.Their study under physiologically relevant conditions remains challenging due to their instability, the requirements of sample preparation and other intrinsic limitations of the techniques used. Advantages of using neutron diffraction and contrast matching to characterize biomaterials are highlighted in this article. We have applied these methods and complementary techniques to search for long-range order within nanoclusters of calcium phosphate sequestered by bovine phosphopeptides, derived from osteopontin or casein. Hydrated and dried samples with different nanocluster radii were analyzed and compared to samples of known calcium phosphate phases. The absence of a distinct diffraction pattern from the nanoclusters is consistent with the presence of amorphous calcium phosphate structure.

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“…Although the structural details are still being elucidated, the casein micelles are believed to be roughly spherical particles with a radius of ϳ100 nm, dispersed in a continuous phase of water, salt, lactose, and whey proteins (4). The calcium phosphate isolated after exhaustive hydrazine deproteination of micelles has been reported to exhibit a fine and uniform granularity under the electron microscope with the particles consisting of small subunits of 2.5-nm diameter (5,6). The calcium phosphate, present as nanometer-sized ion clusters, and caseins are not covalently bound; hence the casein micelle is known as an association colloid (7).…”

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confidence: 99%

Physicochemical Characterization of Casein Phosphopeptide-Amorphous Calcium Phosphate Nanocomplexes

Cross

Huq

Palamara

et al. 2005

Journal of Biological Chemistry

234

183

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Milk caseins stabilize calcium and phosphate ions and make them available to the neonate. Tryptic digestion of the caseins yields phosphopeptides from their polar Nterminal regions that contain clusters of phosphorylated seryl residues. These phosphoseryl clusters have been hypothesized to be responsible for the interaction between the caseins and calcium phosphate that lead to the formation of casein micelles. The casein phosphopeptides stabilize calcium and phosphate ions through the formation of complexes. The calcium phosphate in these complexes is biologically available for intestinal absorption and remineralization of subsurface lesions in tooth enamel. We have studied the structure of the complexes formed by the casein phosphopeptides with calcium phosphate using a range of physicochemical techniques including x-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and equilibrium binding analyses. The amorphous nature of the calcium phosphate phase was confirmed by two independent methods: x-ray powder diffraction and selected area diffraction. In solution, the ion activity product of a basic amorphous calcium phosphate phase was the only ion product that was a function of bound phosphate independent of pH, consistent with basic amorphous calcium phosphate being the phase stabilized by the casein phosphopeptides. Detailed investigations of calcium and calcium phosphate binding using a library of synthetic homologues and analogues of the casein phosphopeptides have revealed that although the fully phosphorylated seryl-cluster motif is pivotal for the interaction with calcium and phosphate, other factors are also important. In particular, calcium binding and calcium phosphate stabilization by the peptides was influenced by peptide net charge, length, and sequence.Bovine milk contains ϳ30 mM calcium and 22 mM inorganic phosphate in solution with most of the calcium (68%) and phosphate (47%) associated with the proteins ␣ S1 -, ␣ S2 -, ␤-, and -casein in casein micelles (1, 2). The ␣ S1 -, ␣ S2 -, and ␤-caseins have a number of Ser(P) residues in a specific motif, Ser(P) 3 -Glu 2 , that is involved in the interaction with calcium phosphate (3).Many techniques have been used to investigate the ultrastructure of the casein micelles. Although the structural details are still being elucidated, the casein micelles are believed to be roughly spherical particles with a radius of ϳ100 nm, dispersed in a continuous phase of water, salt, lactose, and whey proteins (4). The calcium phosphate isolated after exhaustive hydrazine deproteination of micelles has been reported to exhibit a fine and uniform granularity under the electron microscope with the particles consisting of small subunits of 2.5-nm diameter (5, 6). The calcium phosphate, present as nanometer-sized ion clusters, and caseins are not covalently bound; hence the casein micelle is known as an association colloid (7). Nevertheless, the casein micelles are extremely stable and can withstand boiling, freeze-drying, and the add...

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Composition and ultrastructure of calcium phosphate-citrate complexes in bovine milk systems

Cited by 65 publications

References 14 publications

The minerals of milk

The minerals of milk

Structural studies of hydrated samples of amorphous calcium phosphate and phosphoprotein nanoclusters

Physicochemical Characterization of Casein Phosphopeptide-Amorphous Calcium Phosphate Nanocomplexes

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