GTPases are a large family of hydrolase
enzymes that can bind and hydrolyze guanosine triphosphate (GTP). The GTP
binding and hydrolysis takes place in the highly conserved G domain common to
all GTPases. The hydrolysis of the γ phosphate of GTP into guanosine
diphosphate (GDP) and Pi, inorganic phosphate, occurs by the SN2 mechanism (see
nucleophilic substitution) via a pentavalent intermediate state and is
dependent on the magnesium ion Mg2+.