Catalyzes two activities which are involved in the cyclic version of arginine biosynthesis: the synthesis of acetylglutamate from glutamate and acetyl-CoA, and of ornithine by transacetylation between acetylornithine and glutamate. L-glutamate + N(2)-acetyl-L-ornithine = L-ornithine + N-acetyl-L-glutamate acetyl-CoA + L-glutamate = CoA + H(+) + N-acetyl-L-glutamate 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. Amino-acid biosynthesis; L-arginine biosynthesis; N(2)-acetyl-L-ornithine from L-glutamate: step 1/4. Heterodimer of an alpha and a beta chain. The alpha and beta chains are autoproteolytically processed from a single precursor protein within the mitochondrion. Belongs to the ArgJ family.