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Pb2 and Hg2 binding to α‐lactalbumin
Author(s) -
Veprintsev Dmitry B.,
Permyakov Eugene A.,
Kalinichenko Lina. P.,
Berliner Lawrence J.
Publication year - 1996
Publication title -
iubmb life
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.132
H-Index - 113
eISSN - 1521-6551
pISSN - 1521-6543
DOI - 10.1080/15216549600201452
Subject(s) - chemistry , lactalbumin , binding site , histidine , crystallography , stereochemistry , biophysics , biochemistry , enzyme , biology
Interactions of human α‐lactalbumin with Pb2+ and Hg2+ were studied by intrinsic protein fluorescence. Lead ions bind to the strong Ca2+ binding site of α‐lactalbumin (association constant Kass≈2×106 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≈105 M‐1 and some secondary binding site(s) (which probably contain histidine residues) with apparent Kass≈104 M‐1, causing pronounced aggregation of the protein. Mercury ions bind to α‐lactalbumin at the primary Zn2+ sites with Kass≈(1‐4)×104 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 Ca2+‐loaded protein and in some conditions causes pronounced protein aggregation.