P

GTP bound to Gsa is hydrolyzed by the protein's intrinsic GTPase; Gsa thereby turns itself off. The inactive a subunit reassociates with the bg subunit.

FIGURE 12-14 Self-inactivation of Gs. The steps are further described in the text. The protein's intrinsic GTPase activity, in many cases stimulated by RGS proteins (regulators of G protein signaling), determines how quickly bound GTP is hydrolyzed to GDP and thus how long the G protein remains active.

Inactive PKA

Regulatory subunits: empty cAMP sites

Catalytic subunits: substrate-binding sites blocked by autoinhibitory domains of R subunits

Regulatory subunits: autoinhibitory domains buried

Active PKA

Catalytic subunits: open substrate-binding sites

Inactive PKA

Regulatory subunits: empty cAMP sites

Catalytic subunits: substrate-binding sites blocked by autoinhibitory domains of R subunits

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