Crespo J L, Guerrero M G, Florencio F J
Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Sevilla, Spain.
Eur J Biochem. 1999 Dec;266(3):1202-9. doi: 10.1046/j.1432-1327.1999.00992.x.
The role of Asp51 in the catalytic activity of glutamine synthetase from the cyanobacterium Anabaena azollae has been analyzed. Five mutant enzymes, D51S, D51A, D51E, D51N and D51R, were constructed by site-directed mutagenesis and characterized. Asp51 appears to participate in the binding of ammonium ion, as affinity for this substrate was affected in all cases, although it varied according to the charge and/or size of the amino-acid residue, decreasing in the order Glu > Asn > Ser > Ala. The replacement of Asp51 by Glu (D51E) conferred besides a high resistance to the herbicides L-methionine-DL-sulfoximine and phosphinothricin, as a result of a decreased phosphorylation ability.
已对来自满江红鱼腥藻的谷氨酰胺合成酶中Asp51在催化活性中的作用进行了分析。通过定点诱变构建了5种突变酶，即D51S、D51A、D51E、D51N和D51R，并对其进行了表征。Asp51似乎参与铵离子的结合，因为在所有情况下对该底物的亲和力都受到影响，尽管其根据氨基酸残基的电荷和/或大小而有所不同，按Glu>Asn>Ser>Ala的顺序降低。用Glu取代Asp51（D51E）除了赋予对除草剂L-甲硫氨酸-DL-亚砜亚胺和草铵膦的高抗性外，还导致磷酸化能力降低。
