Casein calcium binding

Colloidal calcium phosphate (CCP) acts as a cement between the hundreds or even thousands of submicelles that form the casein micelle. Binding may be covalent or electrostatic. The casein micelles are not static there are three dynamic equilibria between the micelle and its surroundings ... 

Figure 3.24. Calcium binding in 3% /3-casein dispersion at TI2 = 0.14, pH 7.0 and 2°C, as determined by the resin contact time and murexide methods. Apparent maximum number of sites = 11.2 moles of calcium per mole. Apparent intrinsic binding constant = 76.62 liters/mole. (From Jaynes and Whitney 1982. Reprinted with permission of the American Dairy Science Association.)...

Casein exists in milk as a calcium caseinate-calcium phosphate complex the ratio of these components is approximately 95.2 to 4.8. The dispersed casein particles appear to be spherical m shape and of various sizes. The size distribution of the casein micelles is nol constant, hut varies with aging, heating, concentration, and other processing treatments. Processing alters ihe water-binding of casein and this in turn affects the apparent viscosity of products that contain casein Changes in hydration have not been measured quantitatively although the casein panicles of raw milk... 

Park, O. and Allen, J.C. 1998. Preparation of phosphopeptides derived from as-casein and (3-casein using immobilized glutamic acid-specific endopeptidase and characterization of their calcium binding. J. Dairy Sci. 81, 2858-2865. 

The functional properties of milk proteins in foods have recently been expertly treated by Holt and Roginski (2001). These authors described the antihypersensitive, opioid, immunomodulatory, and calcium-binding milk peptides, the antiviral properties of various milk components, and the antimicrobial activity of lactoperoxidase, lactoferrin, lactoferricins, casein peptides, and peptides from a-lactalbumin. 

K-casein on the other (31). Moreover, these simple systems show appreciable differences from native casein micelles in their response to Ca ". In casein micelles, the binding sites for Ca appear to be some distance from the surface of the hairy layer (13) and the same argument can be presumably used for the individual caseins, and show that the calcium binding sites in the synthetic particles are within the surface of shear. On the other hand, the binding of Ca may cause conformational changes in the interfacial layer. 

Osi-casein fraction 194-199 showing immunomodulatory and ACE-inhibitory activity, the opioid peptides a- and P-lactorphin also exhibiting ACE-inhibitory activity and the calcium-binding phos-phopeptides (CPPs), which possess immunomodulatory properties [87]. 

Fig. 10.1. Calcium binding by I agi-casein (0.38), II p-casein (0.21) and III /c-casein (0.05). The bound phosphate residues in mmol/g of casein are given in brackets (according to Walstra and Jenness, 1984)...

Figure 1. Structural features of dog calnexin, mouse calmegin, and rabbit calreticulin. Segments of sequence similarity are represented by the white boxes and the two tandemly repeated sequence motifs are indicated by the numbers 1 and 2. Sites of high affinity calcium binding (Ca +), oligosaccharide binding, and phosphorylation by casein kinase II (C.K. II) are shown. ER localization sequences are indicated at the C-terminus of each protein.

Figure 6.1 The dual binding model of the structure of the casein micelle as built up from the individual caseins (0 1, o 2, P and k) in combination with calcium phosphate (CaP). Reproduced from Home (1998) with permission.

As discussed in Chapter 4 (p. 186), Holt (1994) has proposed that casein has evolved with the ability to bind high concentrations of calcium and phosphate so that milk can contain high levels of these ions, which are essential for neonatal growth, without precipitation in the ducts of the mammary glands. 

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