catalyzes the conversion of N-acetylglutamate-gamma-semialdehyde (NAGSA) to N-acetylornithine in arginine biosynthesis. 2-oxoglutarate + N(2)-acetyl-L-ornithine = L-glutamate + N-acetyl-L-glutamate 5-semialdehyde Amino-acid biosynthesis; L-arginine biosynthesis; N(2)-acetyl-L-ornithine from L-glutamate: step 4/4. The reaction catalyzed by ACOAT is highly reversible. Moreover this enzyme may transaminate ornithine, although this activity should be of little importance at physiological pH. Present with 2300 molecules/cell in log phase SD medium. Belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family.