TAILIEUCHUNG - Báo cáo khoa học: Characterization of acetyl-CoA/propionyl-CoA carboxylase in Metallosphaera sedula Carboxylating enzyme in the 3-hydroxypropionate cycle for autotrophic carbon fixation

Autotrophic Archaea of the family Sulfolobaceae (Cre-narchaeota) use a modified 3-hydroxypropionate cycle for carbon dioxide assimilation. In this cycle the ATP-depend-ent carboxylations of acetyl-CoA and propionyl-CoA to malonyl-CoA and methylmalonyl-CoA,respectively,rep-resent the key CO2fixation reactions. These reactions were studied in the thermophilic and acidophilicMetallosphaera sedula and are shown to be catalyzed by one single large enzyme,which acts equally well on acetyl-CoA and pro-pionyl-CoA | Eur. J. Biochem. 270 736-7M- 2003 FEBS 2003 doi Characterization of acetyl-CoA propionyl-CoA carboxylase in Metallosphaera sedula Carboxylating enzyme in the 3-hydroxypropionate cycle for autotrophic carbon fixation Michael Hiigler Robert S. Krieger Martina Jahn and Georg Fuchs Mikrobiologie Institut fur Biologie II Albert-Ludwigs-Universitut Freiburg Germany Autotrophic Archaea of the family Sulfolobaceae Cre-narchaeota use a modified 3-hydroxypropionate cycle for carbon dioxide assimilation. In this cycle the ATP-depend-ent carboxylations of acetyl-CoA and propionyl-CoA to malonyl-CoA and methylmalonyl-CoA respectively represent the key CO2 fixation reactions. These reactions were studied in the thermophilic and acidophilic Metallosphaera sedula and are shown to be catalyzed by one single large enzyme whih cere equally well on ceetyl-CoA and pro-pionyl-CoA. The carboxylase was purified and characterized and the genes were cloned and seeuenced. In contrast to the carboxylase of most other organisms eve y--CoA porpio-nyl-CoA carboxylase from M. sedula is active at 75 C and is isolated as a stabile functional protein complex of 560 50 kDa. The enzyme consists of two large subunits of 57 kDa each representing biotin carboxylase a and carboxytransferase c vespeetívely mid s mataU kDa biotin carrier protein b . These subunits probably form an abc 4 holoenzyme. It has a catalytic number of 28 s-1 at 65 C and at the optimal pH of . The apparent Km values were mM for acetyl-CoA 0077 mM for propionyl-CoA mM for ATP and mM for bicarbonate. Acetyl-CoA propionyl-CoA carboxylase is considered the main CO2 fixation enzyme of autotrophic members of Sulfolobaceae and the sequenced genomes of these Archaea contain the respective genes. Due to its stability the archaeal carboxylase may prove an ideal subject for further structural studies. Keywords acetyl-CoA carboxylase Archaea autotrophic CO2 fixation 3-hydroxypropionate cycle

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