TABLE 4.

Effect of C2 domain basic- and hydrophobic-to-neutral residue mutations on Ca²⁺ binding affinity

The binding of Ca²⁺ to purified C2 domains (wild type, R216A, R249A, R252A, K268A, W245A, W247A, L191A, or W274A) was measured by monitoring Trp quenching as a function of increasing concentration of Ca²⁺, as described under “Experimental Procedures.” The [Ca²⁺]½ values indicate the weighted averages ± S.E. of at least three independent experiments.

C2α mutation	[Ca2+]1/2	[Ca2+]1/2 with lipid vesicles
	μm	μm
WT	32 ± 4	25.6 ± 0.3
R216A	38 ± 2	46.0 ± 0.8
R249A	1409 ± 69	71 ± 3
R252A	395 ± 27	27.6 ± 0.3
W245A	74 ± 4	567 ± 17
W247A	263 ± 12	188 ± 4