Pb2+ and Hg2+ binding to alpha-lactalbumin.
Interactions of human alpha-lactalbumin with Pb2+ and Hg2+ were studied by intrinsic protein fluorescence. Lead ions bind to the strong Ca2+ binding site of alpha-lactalbumin (association constant Kass approximately 2 x 10(6) M-1) with concomitant spectral changes which are similar to those induced by the binding of Ca2+. Pb2+ also binds to the strong Zn2+ site with Kass approximately 10(5) M-1 and some secondary binding site(s) (which probably contain histidine residues) with apparent Kass approximately 10(4) M-1, causing pronounced aggregation of the protein. Mercury ions bind to alpha-lactalbumin at the primary Zn2+ sites with Kass approximately (1-4) x 10(4) M-1, although the stoichiometry of the binding depends on the conformational state of the protein. Secondary Hg2+ binding sites were suggested to contain histidines, while the strong Hg2+ site contains carboxylates in the coordination sphere and seems to coincide with the strong Zn2+ site. The binding of both Pb2+ and Hg2+ decreases the thermal stability of the Ca(2+)-loaded protein and in some conditions causes pronounced protein aggregation.
Veprintsev
D B
DB
Institute for Biological Instrumentation, Russian Academy of Sciences, Pushchino, Moscow, Russia.
Permyakov
E A
EA
Kalinichenko
L P
LP
Berliner
L J
LJ
D001665:Binding Sites; D002118:Calcium / Q000737:chemistry; D006801:Humans; D007768:Lactalbumin / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D008628:Mercury / Q000737:chemistry*; D011487:Protein Conformation; D011489:Protein Denaturation; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry
D007854:Lead; D007768:Lactalbumin; D008628:Mercury; D015032:Zinc; D002118:Calcium