ITP can act as phosphate donor.

Phosphoenolpyruvate carboxykinase catalyzes the formation of phosphoenolpyruvate by decarboxylation of oxaloacetate while hydrolyzing GTP, a rate limiting step in gluconeogenesis (the biosynthesis of glucose). In vertebrates there are two isozymes: a cytosolic form whose activity is affected by hormones regulating this metabolic process (such as glucagon, or insulin) and a mitochondrial form.

An essential cysteine residue has been proposed to be implicated in the catalytic mechanism; this residue is located in the central part of PEPCK and is in the center of a perfectly conserved region that it's been used as a signature pattern.
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