Acetylornithine aminotransferase TM1785 performs multiple functions in the hyperthermophile Thermotoga maritima.

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 towards 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 towards four amino acids and lyase activity towards l‐cysteine, but no dehydratase activity towards 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. [ABSTRACT FROM AUTHOR]