Calcium binding by α-lactalbumin in human milk and bovine milk

B. Lonnerdal, C. Glazier

Research output: Contribution to journalArticle

37 Citations (Scopus)

Abstract

The metal-binding property of α-lactalbumin (α-LA) in human milk was studied and compared to that of bovine milk α-LA. Gel filtration on Sephadex G-75 at physiological pH and ionic strength separated α-LA in human and bovine milk from most other proteins. The only metal ion associated with α-LA under these conditions was Ca2+. Minor protein contaminants were removed by ion-exchange chromatography, and the ratio of Ca2+:α-LA was determined in the isolated protein preparations. Concentrations of α-LA in mature human milk were between 1.03 and 1.57 mg/ml; the Ca2+ concentration bound to α-LA varied, yielding a molar ratio of Ca2+:α-LA of approximately 1:1 (0.82-1.41 mol Ca2+/mol α-LA) in mature milk. Gel filtration with excess Ca2+ in the running buffer showed that there is another weaker binding site for Ca2+, but this binding does not occur under physiological conditions. Less Ca2+ was bound to bovine α-LA (0.6-0.9 mol Ca2+/mol α-LA) than to human α-LA. Calcium binding was abolished at pH 3.0 and resulted in a substantial increase in the hydrodynamic radius of α-LA. Reconstruction of human α-LA with Ca2+ and other divalent cations at native pH and ionic strength showed a binding specific for Ca2+. Since only 1% of calcium from human milk and 0.15% from bovine milk is α-LA bound, α-LA is probably unimportant with respect to calcium nutrition of the infant. However, the metal binding of α-LA may have a biological significance through its role in the lactose synthase complex.

Original languageEnglish (US)
Pages (from-to)1209-1216
Number of pages8
JournalJournal of Nutrition
Volume115
Issue number9
StatePublished - 1985

Fingerprint

Lactalbumin
lactalbumin
Human Milk
breast milk
Milk
Calcium
calcium
milk
Metals
Osmolar Concentration
Gel Chromatography
Lactose Synthase
Proteins
Divalent Cations
Ion Exchange Chromatography
Hydrodynamics
Buffers
Binding Sites
Ions
ionic strength

ASJC Scopus subject areas

  • Food Science
  • Medicine (miscellaneous)

Cite this

Lonnerdal, B., & Glazier, C. (1985). Calcium binding by α-lactalbumin in human milk and bovine milk. Journal of Nutrition, 115(9), 1209-1216.

Calcium binding by α-lactalbumin in human milk and bovine milk. / Lonnerdal, B.; Glazier, C.

In: Journal of Nutrition, Vol. 115, No. 9, 1985, p. 1209-1216.

Research output: Contribution to journalArticle

Lonnerdal, B & Glazier, C 1985, 'Calcium binding by α-lactalbumin in human milk and bovine milk', Journal of Nutrition, vol. 115, no. 9, pp. 1209-1216.
Lonnerdal, B. ; Glazier, C. / Calcium binding by α-lactalbumin in human milk and bovine milk. In: Journal of Nutrition. 1985 ; Vol. 115, No. 9. pp. 1209-1216.
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