nucleotideexchange

Nucleotideexchange is a term used in biochemistry and molecular biology to describe the process by which a bound nucleotide on a molecule is released and replaced by a different nucleotide. The most common context is nucleotide-binding proteins, particularly small GTPases, that switch between active and inactive forms depending on whether they are bound to GTP or GDP.

In this context, the exchange step is typically rate-limiting: GDP dissociates from the protein, allowing a free nucleotide from the cellular pool, usually abundance of GTP, to bind. The resulting GTP-bound form is active, while hydrolysis of the bound GTP returns the protein to the GDP-bound inactive state. Guanine nucleotide exchange factors (GEFs) catalyze this process by promoting GDP release, whereas GTP hydrolysis and other regulatory proteins such as GTPase-activating proteins (GAPs) and GDP dissociation inhibitors (GDIs) regulate the cycle.

Beyond small GTPases, nucleotideexchange can apply to other nucleotide-binding proteins that undergo similar exchange between nucleotide states, including certain ATPases and other NTPases where the binding of another nucleotide toggles activity. In nucleic acid chemistry, the phrase can also describe exchange or replacement of nucleotides during processes such as repair, editing, or synthesis under specific conditions, though such occurrences are typically described within those specialized contexts rather than as a single universal pathway.

See also: GTPase, GDP, GEF, GAP, Rab, Ras, ATPase, nucleotide binding.