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

B. Lonnerdal, C. Glazier

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37 Scopus citations

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

ASJC Scopus subject areas

  • Food Science
  • Medicine (miscellaneous)

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