-!- The enzyme, characterized from the yeast Saccharomyces cerevisiae Sigma-1278b, N-acetylates L-glutamate-5-semialdehyde, an L-proline biosynthesis/utilization intermediate, into N-acetyl-L-glutamate 5-semialdehyde, an intermediate of L-arginine biosynthesis, under oxidative stress conditions. -!- Its activity results in conversion of L-proline to L-arginine, and reduction in the concentration of L-glutamate 5-semialdehyde and its equilibrium partner, (S)-1-pyrroline-5-carboxylate, which has been linked to production of reactive oxygen species stress. -!- The enzyme also acts on (S)-1-acetylazetidine-2-carboxylate, a toxic L-proline analog produced by some plants, resulting in its detoxification and conferring resistance on the yeast.