Binding Properties of Caltropin

Direct calcium binding assays were carried out using Arsenazo 111 as described by Mani and Kay 

Addition of Ca + resulted in a nearly 15% decrease in the observed tyrosine fluorescence intensity. A plot of the relative fluorescence intensity versus Ca + added indicated the presence of two sets of Ca + binding sites on CaT with Kj values of 2 x 10 and 8 X 10 M and these values are in good agreement with UV difference spectroscopy results. 

FIGURE 5 Ca + binding to caltropin. The binding assay was carried out using the calcium indicator Arsenazo III (Sigma). The solid circles represent the results from the assay. The solvent system used for the assay was 25 mM HEPES buffer, pH 7.5. The solid line represents the best fit of the data. Reprinted with permission from Biochemistry (29). Copyright 1990 American Chemical Society. 

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