Multiple Forms of Glutamate Dehydrogenase in Animals: Structural Determinants and Physiological Implications

Abstract

Glutamate dehydrogenase (GDH) of animal cells is usually considered to be a mitochondrial enzyme. However, this enzyme has recently been reported to be also present in nucleus, endoplasmic reticulum and lysosomes. These extramitochondrial localizations are associated with moonlighting functions of GDH, which include acting as a serine protease or an ATP-dependent tubulin-binding protein. Here, we review the published data on kinetics and localization of multiple forms of animal GDH taking into account the splice variants, post-translational modifications and GDH isoenzymes, found in humans and apes. The kinetic properties of human GLUD1 and GLUD2 isoenzymes are shown to be similar to those published for GDH1 and GDH2 from bovine brain. Increased functional diversity and specific regulation of GDH isoforms due to alternative splicing and post-translational modifications are also considered. In particular, these structural differences may affect the well-known regulation of GDH by nucleotides which is related to recent identification of thiamine derivatives as novel GDH modulators. The thiamine-dependent regulation of GDH is in good agreement with the fact that the non-coenzyme forms of thiamine, i.e., thiamine triphosphate and its adenylated form are generated in response to amino acid and carbon starvation.

Diurnal regulation of the function of the rat brain glutamate dehydrogenase by acetylation and its dependence on thiamine administration

“…As shown in Figure , incubation of mitochondrial GDH in the presence of acetyl‐CoA and NAM inactivates the enzyme in the reductive amination reaction under subsaturating concentrations of either 2‐oxoglutarate (0.1 mM, K M OG 0.9–2.2 mM (Bunik et al, )) or NADH (0.02 mM, K M NADH 0.07–0.12 mM (Bunik et al, )) (Figures b and a). The time‐dependent inactivation of GDH upon incubation with acetyl‐CoA also occurs when measuring the glutamate oxidation (1 mM, K M GLU 2.4–12.4 mM (Bunik et al, )) (Figure c). However, the acetyl‐CoA‐induced inactivation is not observed at saturation (2.5 mM) with 2‐oxoglutarate (Figure d).…”

“…Addition to the assay medium of 1 µM GTP, an allosteric inhibitor of GDH with K i GTP 0.1–1 µM (Bunik et al, ; Frieden, ; Li, Li, Allen, Stanley, & Smith, ), causes about 80% inhibition of the enzyme under the saturating concentrations of 2‐oxoglutarate and NADH (Figure d vs. Figure e).…”

“…Mammalian GDH is regulated by post‐translational modifications, such as phosphorylation, ADP‐ribosylation, and different types of acylation, including acetylation (Bunik et al, ). Mostly, the acetylation is characterized in global studies of the liver tissue, with the GDH acetylation determined along with many other proteins (Lombard et al, ; Lundby et al, ; Zhao et al, ).…”

“…Our analysis of structural data has revealed several acetylatable lysine residues in the vicinity or within the GDH‐binding sites for substrates and allosteric effectors ADP and GTP (Bunik et al, ). For instance, K171 and K183 residues are localized to the 2‐oxoglutarate/glutamate‐binding site (Figure a), K503 residue is localized to the GTP‐binding site (Figure b), whereas K545 and K548 residues of the ADP‐binding site interact with ADP (Figure c).…”

Enzyme Profile of Peripheral Blood Lymphocytes in Patients With the Renal Cell Carcinoma Before and After Surgical Treatment

“…Также следует отметить, что при снижении интенсив-ности гликолиза концентрация пирувата может быть стабилизирована аэробной реакцией ЛДГ, чем, возможно, определяется повышение актив-ности ЛДГ в лимфоцитах периферической крови у больных ПКР в период через 14 дней после хи-рургического лечения. Известно, что НАДН-и НАДФН-зависимые реакции глутаматдегидрогеназ определяют уро-вень оттока интермедиатов с цикла трикар-боновых кислот на метаболические пути ами-нокислотного обмена [11,26]. Обнаруженное повышение активности НАДН-зависимой глу-таматдегидрогеназы в лимфоцитах крови у боль-ных ПКР в период до и после операции отражает увеличение оттока энергетических интермеди-атов на реакции аминокислотного обмена.…”