FIGURE 4.

AKAP79^77–153 specifically competes for binding and inhibition of AC5/6-AKAP79 complexes. A, an IP-AC assay was performed as indicated in the legend for Fig. 1A in the presence of 10 μm AKAP79^77–153 or control polypeptide AKAP79^109–290. The addition of AKAP79^77–153 disrupts associations between AKAP79 and AC5 and -6 but not AC2 or -9. Fsk, forskolin. *, p < 0.05. B, membranes from HEK293 cells expressing AC5 ± AKAP79 were incubated with the indicated concentrations of purified AKAP79^77–153 prior to stimulation with 50 nm Gα_s + 100 μm forskolin. AKAP79^77–153 reverses the inhibition of AC5 by AKAP79 in a concentration-dependent manner. C, the dose-response curve from B indicates an IC₅₀ of 1.0 μm for the reversal of AKAP79 inhibition by AKAP79^77–153. Error bars in A–C indicate mean ± S.E.