Glutamate biosynthesis superpathway

The utilization of ammonia to synthesize glutamate occurs through two pathways in most microorganisms. In the first pathway, glutamate is synthesized through the reductive amination of -ketoglutarate by glutamate dehydrogenase. Two NADPH-dependent glutamate dehydrogenases exist in S. cerevisiae: Gdh1p and Gdh3p. GDH1 is highly expressed when either ethanol or glucose is used as the carbon source, whereas GDH3 is glucose-repressed and induced only in ethanol. The second route of glutamate biosynthesis involves the combined action of glutamine synthetase (Gln1p) and glutamate synthase (Glt1p). In the first step, glutamate reacts with a molecule of ammonia in a reaction catalyzed by Gln1p to form glutamine. In the second, glutamine reacts with -ketoglutarate via Glt1p to form two molecules of glutamate, resulting in a net gain of one for each glutamate molecule that enters the pathway. Source: https://pathway.yeastgenome.org/

在大多数微生物中，利用氨合成谷氨酸的过程通常通过两条途径进行。在第一条途径中，谷氨酸通过谷氨酸脱氢酶对α-酮戊二酸进行还原性胺化而合成。酿酒酵母中存在两种依赖NADPH的谷氨酸脱氢酶：Gdh1p和Gdh3p。当以乙醇或葡萄糖作为碳源时，GDH1的表达量显著增加，而GDH3则在葡萄糖存在下受到抑制，仅在乙醇存在时被诱导。谷氨酸生物合成的第二条途径涉及谷氨酰胺合成酶（Gln1p）和谷氨酸合成酶（Glt1p）的共同作用。在第一步中，谷氨酸与氨分子反应，由Gln1p催化形成谷氨酰胺。在第二步中，谷氨酰胺通过与α-酮戊二酸反应，由Glt1p催化，形成两个谷氨酸分子，从而在每个进入途径的谷氨酸分子中净获得一个。资料来源：https://pathway.yeastgenome.org/