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Calcium-Binding Protein Protocols Calcium-Binding Protein Protocols

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10 Yazawa<br />

Fig. 4. Examples of the Ca 2+ titration curves for the measurements of Ca 2+ -binding<br />

to calmodulin (A), and the resulting Ca 2+ -binding curves (B). Flow dialysis was carried<br />

out on smples of 16.5 µM calmodulin (�), 0.1 M NaCl, and 0.02 M MOPS-NaOH<br />

(pH 7.0) at 25°C at a flow rate of 1 mL/min. Measurements were also carried out in the<br />

presence of target peptide: the 40-kDa fragment of caldesmon (CaD40K, �; 28.5 µM),<br />

and M13 peptide from myosin light chain kinase (�; 43.9 µM). In each titration, 45 Ca 2+<br />

(6.67 × 10 6 cpm for �, �, and 9.73 × 10 6 cpm for �) was added at tube number 7, then<br />

at every six collected tubes, unlabeled Ca 2+ was added successively. During the titration,<br />

1.5–6.6% of 45 Ca 2+ in the sample chamber was lost. The interaction of calmodulin<br />

with CaD40K increases the cooperativity of Ca 2+ -binding, whereas the interaction with<br />

the M13 peptide markedly increases the affinity for Ca 2+ (B), which is differently<br />

reflected in the titration curves (A)

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