Binding of Zn(II) ions to alpha-lactalbumin.
The binding of Zn(II) ions to human and bovine alpha-lactalbumin has been studied by fluorescence, scanning microcalorimetry, and proteolytic digestion. The intrinsic tryptophan fluorescence spectrum of Ca(II)-loaded alpha-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] less than 1) shift heat sorption curves toward lower temperatures. It was concluded that alpha-lactalbumin possess several relatively strong Zn(II) binding sites, which are filled sequentially, the process being accompanied by protein aggregation. The strongest Zn(II) binding (5 x 10(5) 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 alpha-lactalbumin increases its affinity to bis-ANS.
Permyakov
E A
EA
Institute of Biological Physics, U.S.S.R. Academy of Sciences, Pushchino, Moscow Region.
Shnyrov
V L
VL
Kalinichenko
L P
LP
Kuchar
A
A
Reyzer
I L
IL
Berliner
L J
LJ
D000818:Animals; D002152:Calorimetry, Differential Scanning; D002413:Cations, Divalent; D002417:Cattle; D002918:Chymotrypsin / Q000378:metabolism; D005454:Fluorescence Polarization; D006801:Humans; D006868:Hydrolysis; D007768:Lactalbumin / Q000378:metabolism*; D013696:Temperature; D013816:Thermodynamics; D014357:Trypsin / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*
D002413:Cations, Divalent; D007768:Lactalbumin; D002918:Chymotrypsin; D014357:Trypsin; D015032:Zinc