Lara M, Blanco L, Campomanes M, Calva E, Palacios R, Mora J
J Bacteriol. 1982 Apr;150(1):105-12. doi: 10.1128/jb.150.1.105-112.1982.
In Neurospora crassa the assimilation of high and low concentrations of ammonium occurs by two different pathways. When the fungi are growing exponentially on ammonium excess, this compound is fixed by a glutamic dehydrogenase and an octameric glutamine synthetase (GS). The synthesis of this GS polypeptide (beta) is regulated by the nitrogen source present in excess; being higher on glutamate, intermediate on ammonium, and lower on glutamine. When N. crassa is growing in fed-batch ammonium-limited cultures a different polypeptide of GS (alpha), arranged as a tetramer, is synthesized. In both conditions synthesis in vivo correlates with the data obtained with an in vitro translation system primed with N. crassa RNA. This different expression of alpha and beta GS polypeptides was also observed when the cultures were shifted from excess to low nitrogen, and vice versa. By agarose gel electrophoresis in the presence of methylmercury hydroxide, some separation of different mRNAs that direct the in vitro synthesis of alpha and beta GS polypeptides has been accomplished. Data are presented that establish the operation of the tetrameric alpha GS and of glutamate synthase in the assimilation of ammonium in low concentration.
在粗糙脉孢菌中，高浓度和低浓度铵的同化通过两种不同途径进行。当真菌在铵过量的情况下呈指数生长时，这种化合物由谷氨酸脱氢酶和八聚体谷氨酰胺合成酶（GS）固定。这种GS多肽（β）的合成受过量存在的氮源调节；在谷氨酸上含量较高，在铵上处于中间水平，在谷氨酰胺上含量较低。当粗糙脉孢菌在补料分批铵限制培养中生长时，会合成一种不同的GS多肽（α），它排列成四聚体。在这两种情况下，体内合成与用粗糙脉孢菌RNA引发的体外翻译系统获得的数据相关。当培养物从过量氮转移到低氮时，以及反之亦然时，也观察到了α和β GS多肽的这种不同表达。通过在氢氧化甲基汞存在下的琼脂糖凝胶电泳，已实现了一些指导α和β GS多肽体外合成的不同mRNA的分离。所呈现的数据证实了四聚体α GS和谷氨酸合酶在低浓度铵同化中的作用。
