Abstract
The binding of Zn(II) ions to human and bovine α-lactalbumin has been studied by fluorescence, scanning microcalorimetry, and proteolytic digestion. The intrinsic tryptophan fluorescence spectrum of Ca(II)-loaded α-lactalbumin is insensitive to Zn(II) binding to the strong cation binding sites (Zn:protein ratios up to 20), yet the thermal denaturation transition, as detected by intrinsic fluorescence, is shifted toward lower temperatures. On the other hand, low concentrations of Zn(II) ([Zn]:[protein]<1) shift heat sorption curves toward lower temperatures. It was concluded that α-lactalbumin possesses several relatively strong Zn(II) binding sites, which are filled sequentially, the process being accompanied by protein aggregation. The strongest Zn(II) binding (5×105 M−1) increases its susceptibility to tryptic and chymotryptic digestion, slightly decreases its affinity for the fluorescent probe, bis-ANS, and alters its interactions with UDP-galactose. Zn(II) binding to aggregated forms of α-lactalbumin increases its affinity to bis-ANS.
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Permyakov, E.A., Shnyrov, V.L., Kalinichenko, L.P. et al. Binding of Zn(II) ions to α-lactalbumin. J Protein Chem 10, 577–584 (1991). https://doi.org/10.1007/BF01025709
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DOI: https://doi.org/10.1007/BF01025709