TY - JOUR
T1 - Association of the quadruply phosphorylated β-casein from human milk with the nonphosphorylated form
AU - Sood, S. M.
AU - Slattery, C. W.
N1 - CAB Direct platform is the most thorough and extensive source of reference in the applied life sciences, incorporating the leading bibliographic databases CAB Abstracts and Global Health
PY - 2000/12
Y1 - 2000/12
N2 - Human β-casein (β-CN) is phosphorylated at levels from zero (β-CN-0P) to five (β-CN-5P). The major constituent is the 4P form (∼35%), whereas the 0P form (∼5%) has been implicated in the formation of a framework upon which the forms with higher levels of phosphorylation may aggregate. At 4°C in 0.01 M imidazole and 0.02 M NaCl, pH 7, with a 1:1 (wt:wt) 0P:4P ratio and a total protein concentration of 3 mg/ml, the s20,w was 1.4 S (monomer). Laser light scattering gave a radius of ∼4.5 nm. As the temperature, T, increased, s20,w increased to 2 S. At 25°C, peaks of 9.5 S and 2 S were observed. This transition T was different from that of either form. At 37°C, a single peak was again observed with s20,w of 17.5 S, compared with 42 S for the 0P and 14 S for the 4P form. Laser light scattering at 37°C revealed a polymer of ∼16 nm radius and D20,w of 1.55 cm2/s. A combination of D20,w and s20,w gave a relative molecular mass suggesting about 45 monomers per polymer. An incubation of 3 h or more at 37°C caused further aggregation, characteristic of the 0P form, and supported the concept of framework formation. At pH 6.6, s20,w was 38 S compared with 1.4 S at pH 10.4. Hydrostatic pressure did not have a large effect but supported a soap micelle-like structure for the polymer. The turbidity of the mixture increased with the amount of CaCl2 and T until the protein precipitated. The properties of the 1:1 mixture of these human β-CN are intermediate but probably more biased toward those for the 4P form.
AB - Human β-casein (β-CN) is phosphorylated at levels from zero (β-CN-0P) to five (β-CN-5P). The major constituent is the 4P form (∼35%), whereas the 0P form (∼5%) has been implicated in the formation of a framework upon which the forms with higher levels of phosphorylation may aggregate. At 4°C in 0.01 M imidazole and 0.02 M NaCl, pH 7, with a 1:1 (wt:wt) 0P:4P ratio and a total protein concentration of 3 mg/ml, the s20,w was 1.4 S (monomer). Laser light scattering gave a radius of ∼4.5 nm. As the temperature, T, increased, s20,w increased to 2 S. At 25°C, peaks of 9.5 S and 2 S were observed. This transition T was different from that of either form. At 37°C, a single peak was again observed with s20,w of 17.5 S, compared with 42 S for the 0P and 14 S for the 4P form. Laser light scattering at 37°C revealed a polymer of ∼16 nm radius and D20,w of 1.55 cm2/s. A combination of D20,w and s20,w gave a relative molecular mass suggesting about 45 monomers per polymer. An incubation of 3 h or more at 37°C caused further aggregation, characteristic of the 0P form, and supported the concept of framework formation. At pH 6.6, s20,w was 38 S compared with 1.4 S at pH 10.4. Hydrostatic pressure did not have a large effect but supported a soap micelle-like structure for the polymer. The turbidity of the mixture increased with the amount of CaCl2 and T until the protein precipitated. The properties of the 1:1 mixture of these human β-CN are intermediate but probably more biased toward those for the 4P form.
KW - Human milk
KW - Human β-casein
KW - Protein-ion interactions
KW - Protein-protein interactions
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U2 - 10.3168/jds.S0022-0302(00)75172-1
DO - 10.3168/jds.S0022-0302(00)75172-1
M3 - Article
C2 - 11132844
SN - 0022-0302
VL - 83
SP - 2766
EP - 2770
JO - Journal of Dairy Science
JF - Journal of Dairy Science
IS - 12
ER -