Acetylornithine aminotransferase TM1785 performs multiple functions in the hyperthermophile <i>Thermotoga maritima</i>
Tetsuya Miyamoto, Yasuaki Saitoh, Masumi Katane, Masae Sekine, Kumiko Sakai‐Kato, Hiroshi Homma
Abstract
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 ( k cat / K m ) 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.