TABLE 2.

Effect of ionic strength on Ca²⁺ binding to CaM

Apparent K_Ca, Hill coefficients, and k_off rates were determined as described under “Experimental Procedures.” Values are the average ± S.D. of at least three experiments. The k_on was calculated from k_on = k_off/KCa. The buffer is 20 mm MOPS, pH 7.5, with the indicated concentration of KCl. An ionic strength of 13 mm is contributed by 20 mm MOPS at this pH. PEP-19 was added to a final concentration of 30 μm.

KCl	PEP-19	KCa	Hill coefficient	koff	kon
mm		μm		s−1	μm−1 s−1
100	−	1.6 ± 0.1	1.8 ± 0.1	12.5 ± 0.1	7.8
0	−	0.12 ± 0.01	1.8 ± 0.04	7.0 ± 0.2	58
100	+	2.0 ± 0.1	1.1 ± 0.01	428 ± 40	214
0	+	0.14 ± 0.01	1.0 ± 0.05	363 ± 24	2592