Characterization of glutamine synthetase in the apple
Characterization of glutamine synthetase in the apple
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苹果谷氨酰胺合成酶的特性
DOI：
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发表时间：
1981
期刊：
影响因子：
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通讯作者：
J. S. Titus
中科院分区：
文献类型：
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作者：
Seong;J. S. Titus
苹果（Malus domestica Borkh）树皮组织中的谷氨酰胺合成酶（l-glutamate：氨连接酶，ADP-forming, EC 6.3.1.2）。简历。金冠)进行了部分纯化和表征。在pH值为7.2和7.5时，Mn2+和Mg2+依赖性活性最大。在0℃条件下，两周内酶几乎完全失活。Mg2+和β-巯基乙醇在贮藏过程中均具有稳定酶的作用。在60°C时，加入Mg2+和ATP保护酶免于热失活。十分之一毫米苯汞醋酸酯抑制Mg2+依赖性活性50%。等摩尔二硫苏糖醇保护酶免于失活。该酶对ATP、谷氨酸和NH2OH的Km值分别为0.27、7.35和0.69 mM。在Mn2+的存在下，nh4的常数比Mg2+高一个数量级。
Glutamine synthetase (l-glutamate: ammonia ligase, ADP-forming, EC 6.3.1.2) in bark tissue of the apple (Malus domestica Borkh. cv. Golden Delicious) was partially purified and characterized. The Mn2+- and Mg2+-dependent activities were maximal at pH 7.2 and 7.5, respectively. The enzyme was almost completely inactivated within two weeks at 0°C. Both Mg2+ and β-mercaptoethanol were effective in stabilizing the enzyme during storage. The enzyme was protected from thermal inactivation at 60°C by the addition of Mg2+ and ATP. One-tenth mM phenylmercuric acetate inhibited the Mg2+-dependent activity by 50%. Equimolar dithiothreitol protected the enzyme from this inactivation. The Km values of the enzyme were 0.27, 7.35, and 0.69 mM for ATP, glutamate, and NH2OH, respectively. The constant for NH+4 was an order of magnitude higher in the presence of Mn2+ than Mg2+.
When the amino acids were externally added to the reaction mixtures, the measurement of Pi exhibited a higher degree of enzyme inhibition than the measurement of γ-glutamyl monohydroxamate (GHA). Ten mM histidine inhibited the Mg2+- and Mn2+-dependent activities by 26 and 45% respectively. Twenty mM aspartate (d,l-form) inhibited the enzyme 30% in the presence of either Mg2+ or Mn2+. Aspartate (Mg2+-dependent) and histidine (Mn2+-dependent) inhibited the enzyme competitively with respect to glutamate, the estimated inhibition constants being 17.6 and 1.6 mM, respectively. At 10 mM, amino acids such as tryptophan, arginine, alanine and citrulline inhibited enzyme activity from 1 to 18%. Glutamine stimulated the Mg2+-dependent activity 25% at 25 mM when GHA was measured. Glutamine above 32 mM inhibited the enzyme.