Mechanism of arginine biosynthesis in Chlamydomonas reinhardti I. Purification and properties of ornithine acetyltransferase

Maria Staub, G. Dénes
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引用次数: 34

Abstract

  • 1.

    1. Ornithine acetyltransferase (proposed name, α-N-acetyl-l-ornithine:l-glutamateN-acetyltransferase) which catalyzes the first step in arginine biosynthesis, the formation of N-acetylglutamate from α-N-acetyl-l-ornithine and l-glutamate, has been isolated from the freshwater alga Chlamydomonas reinhardti.

  • 2.

    2. The enzyme has a broad pH optimum between 7.5 and 9. The Km value of the enzyme at pH 7.5 is 1.3 · 10−2 M for glutamate and 5.5 · 10 −3 M for α-N-acetyl-l-ornithine. The reaction is reversible; the equilibrium constant expressed as K = [acetylglutamate][ornithine]/[acetylornithine][glutamate] is 0.47.

  • 3.

    3. Beside the transferase activity, the enzyme has also a hydrolytic activity. The rate of the hydrolytic reaction for α-N acetylornithine is 1% of that of the acetyltransferase reaction.

  • 4.

    4. No specific cofactor has been found. The enzyme is inhibited by p-chloromercuribenzoate, but not by iodoacetate.

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莱茵衣藻精氨酸生物合成机制1 .鸟氨酸乙酰转移酶的纯化及性质
1.1. 从莱茵衣藻(Chlamydomonas reinhardti)中分离到一种鸟氨酸乙酰转移酶(拟命名为α- n -乙酰基-l-鸟氨酸:l-谷氨酸乙酰转移酶),它催化精氨酸生物合成的第一步,即α- n -乙酰基-l-鸟氨酸和l-谷氨酸形成n -乙酰谷氨酸。这种酶的最适pH值在7.5到9之间。在pH 7.5时,谷氨酸酶的Km值为1.3·10−2 M, α- n -乙酰-l-鸟氨酸酶的Km值为5.5·10−3 M。反应是可逆的;用K =[乙酰谷氨酸][鸟氨酸]/[乙酰鸟氨酸][谷氨酸]表示的平衡常数为0.47.3.3。除了转移酶活性外,该酶还具有水解活性。α-N乙酰鸟氨酸水解反应速率为乙酰转移酶反应速率的1%。没有发现具体的辅助因子。对氯脲苯甲酸酯对该酶有抑制作用,而碘乙酸对其无抑制作用。
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