Romero J M, Flores E, Guerrero M G
Arch Microbiol. 1985 Jun;142(1):1-5. doi: 10.1007/BF00409227.
In an attempt to establish the nature of the ammonium-assimilation products which mediate the inhibition by ammonium of nitrate uptake in cyanobacteria, the effect of different amino acids on nitrate utilization by intact Anacystis nidulans cells has been assayed. To exclude an indirect inhibition of nitrate uptake through the ammonium which the amino acids might release, the cells were pretreated with L-methionine-D,L-sulfoximine (MSX), a potent inactivator of glutamine synthetase. Under these conditions, several L-amino acids, but not the corresponding D-isomers, affected nitrate utilization to a variable extent, causing inhibitions ranging between 20 and 80% when added at 20 mM concentration. For most of the inhibitory amino acids, including L-isoleucine, L-leucine and L-valine, a correlation was found between their ability to act as amino group donors to alpha-ketoglutarate, in reactions catalyzed by A. nidulans cell-free extracts, and their inhibitory effect on nitrate utilization. L-Glutamine, L-asparagine and glycine, being effective inhibitors of nitrate utilization, were poor substrates for the transaminating activity to alpha-ketoglutarate, however. The possible role of the latter amino acids as mediators in the ammonium-promoted inhibition of nitrate uptake is discussed.
为了确定介导铵对蓝细菌硝酸盐吸收抑制作用的铵同化产物的性质，已检测了不同氨基酸对完整的集胞藻细胞硝酸盐利用的影响。为了排除氨基酸可能释放的铵对硝酸盐吸收的间接抑制作用，细胞先用谷氨酰胺合成酶的有效失活剂L-蛋氨酸-D，L-亚砜亚胺（MSX）进行预处理。在这些条件下，几种L-氨基酸（但相应的D-异构体则不然）在不同程度上影响硝酸盐利用，当以20 mM浓度添加时，抑制率在20%至80%之间。对于大多数抑制性氨基酸，包括L-异亮氨酸、L-亮氨酸和L-缬氨酸，发现在由集胞藻无细胞提取物催化的反应中，它们作为α-酮戊二酸氨基供体的能力与其对硝酸盐利用的抑制作用之间存在相关性。然而，L-谷氨酰胺、L-天冬酰胺和甘氨酸虽然是硝酸盐利用的有效抑制剂，但却是α-酮戊二酸转氨活性的不良底物。讨论了后几种氨基酸作为铵促进硝酸盐吸收抑制作用介质的可能作用。
