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In enzymology, a diphthine—ammonia ligase (EC 6.3.1.14, diphthamide synthase, diphthamide synthetase) is an enzyme that catalyzes the chemical reaction

ATP + diphthine + NH₃ ${\displaystyle \rightleftharpoons }$ ADP + phosphate + diphthamide

The 3 substrates of this enzyme are ATP, diphthine, and NH₃, whereas its 3 products are ADP, phosphate, and diphthamide.

This enzyme belongs to the family of ligases, specifically those forming carbon-nitrogen bonds as acid-D-amino-acid ligases (peptide synthases). The systematic name of this enzyme class is diphthine:ammonia ligase (ADP-forming). Other names in common use include diphthamide synthase, and diphthamide synthetase.

References

• Moehring JM, Moehring TJ (1988). "The post-translational trimethylation of diphthamide studied in vitro". J. Biol. Chem. 263 (8): 3840–4. PMID 3346227.
• Moehring TJ, Moehring JM (1987). "Mutant cultured cells used to study the synthesis of diphthamide". UCLA Symp. Mol. Cell. Biol. New Series. 45: 53–63.

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