Accepted name: N-acetylornithine carbamoyltransferase
Reaction: carbamoyl phosphate + N2-acetyl-L-ornithine = phosphate + N-acetyl-L-citrulline
Glossary: N-acetyl-L-citrulline = N5-acetylcarbamoyl-L-ornithine
Other name(s): acetylornithine transcarbamylase; N-acetylornithine transcarbamylase; AOTC; carbamoyl-phosphate:2-N-acetyl-L-ornithine carbamoyltransferase; AOTCase
Systematic name: carbamoyl-phosphate:N2-acetyl-L-ornithine carbamoyltransferase
Comments: Differs from EC, ornithine carbamoyltransferase. This enzyme replaces EC in the canonic arginine biosynthetic pathway of several Eubacteria and has no catalytic activity with L-ornithine as substrate.
1.  Shi, D., Morizono, H., Yu, X., Roth, L., Caldovic, L., Allewell, N.M., Malamy, M.H. and Tuchman, M. Crystal structure of N-acetylornithine transcarbamylase from Xanthomonas campestris: a novel enzyme in a new arginine biosynthetic pathway found in several Eubacteria. J. Biol. Chem. 280 (2005) 14366–14369. [PMID: 15731101]
2.  Morizono, H., Cabrera-Luque, J., Shi, D., Gallegos, R., Yamaguchi, S., Yu, X., Allewell, N.M., Malamy, M.H. and Tuchman, M. Acetylornithine transcarbamylase: a novel enzyme in arginine biosynthesis. J. Bacteriol. 188 (2006) 2974–2982. [PMID: 16585758]
[EC created 2005]
Accepted name: N-succinylornithine carbamoyltransferase
Reaction: carbamoyl phosphate + N2-succinyl-L-ornithine = phosphate + N-succinyl-L-citrulline
Glossary: N-acetyl-L-citrulline = N5-acetylcarbamoyl-L-ornithine
Other name(s): succinylornithine transcarbamylase; N-succinyl-L-ornithine transcarbamylase; SOTCase
Systematic name: carbamoyl phosphate:N2-succinyl-L-ornithine carbamoyltransferase
Comments: This enzyme is specific for N-succinyl-L-ornithine and cannot use either L-ornithine (see EC, ornithine carbamoyltransferase) or N-acetyl-L-ornithine (see EC, N-acetylornithine carbamoyltransferase) as substrate. However, a single amino-acid substitution (Pro90 → Glu90) is sufficient to switch the enzyme to one that uses N-acetyl-L-ornithine as substrate. It is essential for de novo arginine biosynthesis in the obligate anaerobe Bacteroides fragilis, suggesting that this organism uses an alternative pathway for synthesizing arginine.
1.  Shi, D., Morizono, H., Cabrera-Luque, J., Yu, X., Roth, L., Malamy, M.H., Allewell, N.M. and Tuchman, M. Structure and catalytic mechanism of a novel N-succinyl-L-ornithine transcarbamylase in arginine biosynthesis of Bacteroides fragilis. J. Biol. Chem. 281 (2006) 20623–20631. [PMID: 16704984]
2.  Shi, D., Yu, X., Cabrera-Luque, J., Chen, T.Y., Roth, L., Morizono, H., Allewell, N.M. and Tuchman, M. A single mutation in the active site swaps the substrate specificity of N-acetyl-L-ornithine transcarbamylase and N-succinyl-L-ornithine transcarbamylase. Protein Sci. 16 (2007) 1689–1699. [PMID: 17600144]
[EC created 2008]