Fayyaz-Chaudhary M, Javed Qamar, Merrett Michael J
Department of Botany and Microbiology, University College, Singleton Park, Swansea SA2 8PP, UK.
New Phytol. 1985 Nov;101(3):367-376. doi: 10.1111/j.1469-8137.1985.tb02843.x.
Cells of Euglena gracilis Klebs, strain z Pringsheim, had high NADPH-glutamate dehydrogenase (GDH) activity when grown on glutamate but activity was repressed completely in cells grown on ammonium (NH ). Subcellular fractionation showed that NADPH-GDH activity was located exclusively in the cytosol, while glutamine synthetase was present in the cytosol and chloroplasts. Despite high NADPH-GDH activity NH assimilation was completely inhibited by methionine sulphoximine (MSO), an inhibitor of glutamine synthetase. With MSO present, cells produced NH and it was shown that greatest NH production occurred with cells containing high levels of NADPH-GDH activity and plentiful carbon supply. It is concluded that NADPH-GDH has a catabolic function in Euglena generating NH from glutamate under conditions of nitrogen limitation.
纤细裸藻（Euglena gracilis Klebs）z Pringsheim品系的细胞在以谷氨酸为生长底物时具有较高的NADPH-谷氨酸脱氢酶（GDH）活性，但在以铵（NH₄⁺）为生长底物的细胞中该活性被完全抑制。亚细胞分级分离显示，NADPH-GDH活性仅存在于细胞质中，而谷氨酰胺合成酶存在于细胞质和叶绿体中。尽管NADPH-GDH活性较高，但蛋氨酸亚砜亚胺（MSO，一种谷氨酰胺合成酶抑制剂）完全抑制了NH₄⁺的同化作用。在存在MSO的情况下，细胞产生了NH₄⁺，并且表明，在含有高水平NADPH-GDH活性和充足碳源的细胞中，NH₄⁺的产生量最大。得出的结论是，在氮限制条件下，NADPH-GDH在裸藻中具有分解代谢功能，可从谷氨酸生成NH₄⁺。
