GTPase-activating protein

CAP (eng: GTPase -activating proteins) are proteins that act on G- proteins such that they bound their GTP hydrolysis with elimination of a phosphate moiety to GDP. In most cases, the target protein is thus disabled, as it is only active in the GTP-bound form. The G- proteins themselves are GTPases. As the name suggests, the GAPs accelerate the process of GTP hydrolysis only, and the reaction would take place without the GAPs. However, it is important to most processes in the cell, that the activated G- proteins can be turned off quickly. The " turnover " is the faster, the faster changes may be noticeable.

The GAPs are the opponents of the GTP exchange factors ( GEFs ), which have exactly the opposite effect.