J. Biol. Chem., Vol. 262, Issue 7, 3196-3198, 03, 1987
On experimental artifacts in the use of metal ion chelators for the determination of the cation binding constants of alpha-lactalbumin. A reply
EA Permyakov, K Murakami and LJ Berliner
The binding constant of Ca2+ to the strong cation site of bovine alpha-
lactalbumin has been measured directly by monitoring the free calcium
concentration by Quin 2 fluorescence. A dissociation constant of 1-4 nM was
calculated, which confirms the strong calcium binding properties of this
protein. In order to examine whether the metal ion chelators EDTA or EGTA
affect the cation binding equilbria by binding to bovine alpha-
lactalbumin, calcium binding equilibria were carefully measured under
highly stabilized pH and temperature conditions. Within the concentration
ranges required for competitive binding by these ligands (EDTA or EGTA)
(less than 1-3 mM) these chelators produced no artifacts, in contradiction
to the data of Kronman and Bratcher (Kronman, M. J., and Bratcher, S. C.
(1983) J. Biol. Chem. 258, 5707- 5709).