Open AccessA Study of the Interaction of Calcium Ions with Bovine α s1 ‐Casein Using Fluorescence Spectroscopy
Author(s) -
Dalgleish Douglas G.
Publication year - 1973
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1973.tb03207.x
Subject(s) - tryptophan , chemistry , fluorescence , calcium , casein , fluorescence spectroscopy , precipitation , ion , biophysics , crystallography , biochemistry , amino acid , organic chemistry , biology , physics , quantum mechanics , meteorology
The interaction of α s1 ‐casein with calcium ions at pH 7.0 has been studied, and it is shown that there is a stepwise increase in the fluorescence of the tryptophan residues of the protein as increasing amounts of Ca 2+ are added, leading to eventual precipitation of the calcium‐caseinate complex. The first of these steps appears to result from a conformational change induced by Ca 2+ , without which the protein cannot precipitate. Further steps arise from interaction between protein molecules to produce particles of about 120 nm in diameter, then final aggregation of these particles to give a precipitate. All of these changes result in changes in the fluorescence emission spectra of one or both tryptophan residues in the casein, although most of the change in fluorescence behaviour in the first step of the interaction probably arises from tryptophan‐164 in the protein: