EC 2.1.3.9     
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 2.1.3.3, ornithine carbamoyltransferase. This enzyme replaces EC 2.1.3.3 in the canonic arginine biosynthetic pathway of several Eubacteria and has no catalytic activity with L-ornithine as substrate.
References:
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 2.1.3.9 created 2005]
 
 
EC 2.1.3.11     
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 2.1.3.3, ornithine carbamoyltransferase) or N-acetyl-L-ornithine (see EC 2.1.3.9, 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.
References:
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 2.1.3.11 created 2008]