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Figure 5.
Figure 5 Effect of calcium and magnesium ions on adenylyl
cyclase activity of EF and CyaA-N (A and B) and an EF mutant,
EF-H577N (C and D). Adenylyl cyclase activity assays were
performed with 10  M
CaM at 0.1 M
Ca^2+ (filled circles), 0.3 M
Ca^2+ (open circles) and 1.0 M
Ca^2+ (filled triangles) in the presence of 1 nM EF (A), and 0.7
nM CyaA-N (B). To analyze the mutant form of EF, adenylyl
cyclase activities were measured with 10 M
CaM and 1 nM EF or 66 nM EF-H577N with either 0.3 M
Ca^2+ (C) or 10 mM Mg^2+ (D). Both were buffered by 10 mM EGTA.
Maximal activities for EF in the magnesium titration are 1616
s^-1 (0.1 M
Ca^2+), 1074 s^-1 (0.3 M
Ca^2+), and 1009 s^-1 (1.0 M
Ca^2+) (A) and those for CyaA-N are 2106 s^-1 (0.1 M
Ca^2+), 1674 s^-1 (0.3 M
Ca^2+) and 1385 s^-1 (1.0 M)
(B). Maximal activities for EF and EF-H577N were 1208 s^-1 and 4
s^-1 (C) and those for EF and EF-H577N were 2726 s^-1 and 6 s^-1
(D), respectively. Means  SE
are representative of at least two experiments.
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