Now, once we form the GTP molecule, the GTP is generally used for two purposes. They can either be used by g proteins for instance, we saw that in signal transduction pathways we have g proteins and the g proteins utilize the GTP molecule and so we can use it for that specific purpose or the GTP can actually be transformed into ATP. How? Well, by the action of an enzyme known as nucleotide diphosphokinase. This enzyme actually catalyzes the transfer of a phosphoryl group from the GTP onto an ADP to form the ATP and this GDP. So in this process we utilize the GTP form in step five of the citric acid cycle to generate ATP molecules that can be used by a variety of processes inside our body.