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Carbamoyl phosphate synthetase catalyzes the ATP-dependent synthesis of carbamoyl phosphate from glutamine () or ammonia () and bicarbonate. This enzyme catalyzes the reaction of ATP and bicarbonate to produce carbamoyl phosphate and ADP. Carboxy phosphate reacts with ammonia to give carbamate. In turn, carbamate reacts with a second ATP to give carbamoyl phosphate plus ADP. It represents the first committed step in pyrimidine and arginine biosynthesis in prokaryotes and eukaryotes, and in the urea cycle in most terrestrial vertebrates. Most prokaryotes carry one form of CPSase that participates in both arginine and pyrimidine biosynthesis, however certain bacteria can have separate forms. There are three different forms that serve very different functions: * Carbamoyl phosphate synthetase I (mitochondria, urea cycle) * Carbamoyl phosphate synthetase II (cytosol, pyrimidine metabolism). * Carbamoyl phosphate synthetase III (found in fish). ==Mechanism== Carbamoyl phosphate synthase has three main steps in its mechanism and is, in essence, irreversible.〔Biochemistry, 3rd edition, J.M. Berg, J.L. Tymoczko, L. Stryer〕 # Bicarbonate ion is phosphorylated with ATP to create carboxylphosphate. # The carboxylphosphate then reacts with ammonia to form carbamic acid, releasing inorganic phosphate. # A second molecule of ATP then phosphorylates carbamic acid, creating carbamoyl phosphate. The activity of the enzyme is known to be inhibited by both Tris and HEPES buffers. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Carbamoyl phosphate synthetase」の詳細全文を読む スポンサード リンク
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