N-acetyltransferase involved in oxidative stress resistance. Acetylates the toxic proline metabolism intermediate (S)-1-pyrroline-5-carboxylate (P5C), or more likely its spontaneously forming tautomer glutamate-5-semialdehyde (GSA) into N-acetyl-GSA for arginine synthesis in the mitochondria. P5C has been shown to increase the levels of reactive oxigen species (ROS) in the cell by inhibiting the function of the respiratory chain in the mitochondria. The enzyme is able to reduce intracellular ROS levels under P5C-induced oxidative stress and protects cells from damage by oxidative stress (PubMed:15308773, PubMed:20550582, PubMed:22698729). Also acetylates and thereby detoxifies the proline analog azetidine-2-carboxylate (AZC), however it is unlikely that AZC is a natural substrate as it occurs only in plants belonging to the Lilaceae family (PubMed:11555637). Does not acetylate proline (PubMed:11555637, PubMed:12761200). acetyl-CoA + L-glutamate 5-semialdehyde = CoA + H(+) + N-acetyl-L-glutamate 5-semialdehyde kcat is 17.9 sec(-1) with azetidine-2-carboxylate as substrate and 121 sec(-1) with (S)-1-pyrroline-5-carboxylate as substrate. Optimum pH is 8.5-9 for azetidine-2-carboxylate and 6.5-7 for (S)-1-pyrroline-5-carboxylate. Optimum temperature is 35 degrees Celsius. Homodimer. Not glycosylated. Belongs to the acetyltransferase family.