LAUSR

The hyperthermophilic bacterium Thermotoga maritima peptidoglycan contains unusual D-lysine alongside typical D-alanine and D-glutamate. We previously identified lysine racemase and threonine dehydratase, but knowledge of D-amino acid metabolism remains limited. Herein, we identified and characterized T. maritima acetylornithine aminotransferase TM1785. The enzyme was most active toward acetyl-L-ornithine, but also utilized L-glutamate, L-ornithine, and acetyl-L-lysine as amino donors, and 2-oxoglutarate was the preferred amino acceptor. TM1785 also displayed racemase activity toward four amino acids and lyase activity toward L-cysteine, but no dehydratase activity toward L-serine, L-threonine, or corresponding D-amino acids. Catalytic efficiency (kcat /Km ) was highest for aminotransferase activity and lowest for racemase activity. TM1785 is a novel acetylornithine aminotransferase associated with L-arginine biosynthesis that possesses two additional distinct activities.