Interaction Of Zn(II) With Bovine Milk A-Casein: Structure–Function Study

a-Casein is the major casein from bovine milk, responsible for binding to
metal ions. Interaction of a-casein with Zn(II) studied by equilibrium dialysis
indicates the presence of 17.0 � 2.0 binding sites for Zn(II) with two association
constants ka1 0.2 � 0.03 ¥ 106 M–1 and ka2 2.7 � 0.3 ¥ 106 M–1, respectively.
Far-Ultraviolet Circular dichroic measurement shows formation of
secondary structures in the presence of Zn(II). Fluorescence quenching studies
by acrylamide shows blue shift in the emission maxima and decreased Stern–
Volmer constant from 10.4 to 4.1 M-1. The kinetics of binding as analyzed by
stopped flow shows pseudo-first-order rate of 37 � 5 s-1. Holistically, this
interaction leads to formation of stable complexes, useful for fortification of
milk-based products with micronutrient zinc.