Catalyzes only the synthesis of N-acetylglutamate from glutamate and acetyl-CoA as the acetyl donor. L-glutamate + N(2)-acetyl-L-ornithine = L-ornithine + N-acetyl-L-glutamate Competitively inhibited by L-ornithine. Optimum pH is 8. Optimum temperature is above 95 degrees Celsius. Amino-acid biosynthesis; L-arginine biosynthesis; L-ornithine and N-acetyl-L-glutamate from L-glutamate and N(2)-acetyl-L-ornithine (cyclic): step 1/1. Heterotetramer of two alpha and two beta chains. Some bacteria possess a monofunctional ArgJ, i.e. capable of catalyzing only the fifth step of the arginine biosynthetic pathway. Belongs to the ArgJ family.