-!- This enzyme comprises a family of proteins involved in prokaryotic as well as eukaryotic protein synthesis. -!- In the initiation factor complex, it is IF-2b (98 kDa) that binds GTP and subsequently hydrolyzes it in prokaryotes. -!- In eukaryotes, it is eIF-2 (150 kDa) that binds GTP. -!- In the elongation phase, the GTP-hydrolyzing proteins are the EF-Tu polypeptide of the prokaryotic transfer factor (43 kDa), the eukaryotic elongation factor EF-1-alpha (53 kDa), the prokaryotic EF-G (77 kDa), the eukaryotic EF-2 (70-110 kDa) and the signal recognition particle that play a role in endoplasmic reticulum protein synthesis (325 kDa). -!- EF-Tu and EF-1-alpha catalyze binding of aminoacyl-tRNA to the ribosomal A-site, while EF-G and EF-2 catalyze the translocation of peptidyl-tRNA from the A-site to the P-site. -!- GTPase activity is also involved in polypeptide release from the ribosome with the aid of the pRFs and eRFs. -!- Formerly EC 3.6.1.48.