Glutamate dehydrogenase (GDH) plays a key role in the metabolism of glutamate, an important compound at a cross-road of carbon and nitrogen metabolism and a relevant neurotransmitter. Despite being one of the first discovered allosteric enzymes, GDH still poses challenges for structural characterization of its allosteric sites. Only the structures with ADP, and at low (3.5 Å) resolution, are available for mammalian GDH complexes with allosteric activators. Here we aim at deciphering structural basis for the GDH allosteric activation, using bovine GDH as a model. For the first time we report a mammalian GDH structure in a ternary complex with the activators leucine and ADP, co-crystallized with potassium ion. An improved 2.4 Å resolution of the GDH complex with ADP is also presented. The ternary complex with leucine and ADP differs from the binary complex with ADP by the conformation of GDH C-terminus, involved in the leucine binding and subunit interactions. The potassium site, identified in this work, may mediate interactions between the leucine and ADP binding sites. Our data provide novel insights into the mechanisms of GDH activation by leucine and ADP, linked to the enzyme regulation by (de)acetylation.

Transketolase (TKT) is an essential thiamine diphosphate (ThDP)-dependent enzyme of the non-oxidative branch of pentose phosphate pathway, with the glucose-6P flux through the pathway regulated in various medically important conditions. Here, we characterize the brain TKT regulation by acylation in rats with perturbed thiamine-dependent metabolism, known to occur in neurodegenerative diseases. The perturbations are modelled by administration of oxythiamine inhibiting ThDP-dependent enzymes in vivo, or by reduced thiamine availability in the presence of metformin and amprolium, inhibiting intracellular thiamine transporters. Compared to control rats, chronic administration of oxythiamine does not significantly change the modification level of the two detected TKT acetylation sites (K6 and K102), but doubles malonylation of TKT K499, concomitantly decreasing 1.7-fold the level of demalonylase sirtuin 5. The inhibitors of thiamine transporters do not change average levels of TKT acylation or sirtuin 5. TKT structures indicate that the acylated residues are distant from the active sites. The acylations-perturbed electrostatic interactions may be involved in conformational shifts and/or formation of TKT complexes with other proteins or nucleic acids. Acetylation of K102 may affect the active site entrance/exit and subunit interactions. Correlation analysis reveals that the action of oxythiamine is characterized by significant negative correlations of K499 malonylation or K6 acetylation with TKT activity, not observed upon the action of the inhibitors of thiamine transport. However, the transport inhibitors induce significant negative correlations between the TKT activity and K102 acetylation or TKT expression, absent in the oxythiamine group. Thus, perturbations in the ThDP-dependent catalysis or thiamine transport manifest in the insult-specific patterns of the brain TKT malonylation and acetylations.

Mitochondrial pyruvate dehydrogenase complex (PDHC) is essential for the brain glucose and neurotransmitter metabolism, dysregulated in many pathologies. Using specific inhibitors of PDHC in vivo, we determine biochemical and physiological responses to PDHC dysfunction. Dose dependence of the responses to membrane-permeable dimethyl acetylphosphonate (Ac-PMe2) is non-monotonous. Primary decreases in glutathione and its redox potential, methionine and ethanolamine are alleviated with increasing PDHC inhibition, the alleviation accompanied by physiological changes. Comparison of 39 brain biochemical parameters after administration of four phosphinate and phosphonate analogs of pyruvate at a fixed dose of 0.1 mmol/kg reveals no primary, but the secondary changes, such as activation of 2-oxoglutarate dehydrogenase complex (OGDHC) and decreased levels of glutamate, isoleucine and leucine. The accompanying decreases in RMSSD of ECG and freezing time are most pronounced after administration of me-thyl acetylphosphinate and dimethyl acetylphosphonate. The levels of PDHA1 expression and phosphorylation, sirtuin 3 and total protein acetylation are not significantly changed by the PDHC inhibitors that affect the brain protein succinylation and glutarylation. Thus, decreased production of the tricarboxylic acid cycle substrate acetyl-CoA by inhibited PDHC is compen-sated by increased degradation of amino acids through the cycle with activated OGDHC, increas-ing total protein succinylation and decreasing anxiety indicators.

Disturbed metabolism of vitamins B1 or B6, which are essential for neurotransmitters homeostasis, may cause epilepsy. Our study aims at revealing therapeutic potential of vitamins B1 and B6 in epilepsy by estimating effects of their combined administration on a seizure and its consequences in rats subjected to pentylenetetrazole (PTZ). The PTZ dose dependence of a seizure and its parameters according to Racine’s scale along with delayed physiological and biochemical consequences next day after the seizure are assessed regarding sexual dimorphism in epilepsy. PTZ sensitivity is stronger in the female than male rats. Next day after a seizure, gender differences in behavior and brain biochemistry arise. The induced gender differences in anxiety, exploratory and locomotor activity correspond to disappearance of gender differences in the brain GABA, aspartate, alanine and serine, with appearance of those in glutamate, glutamine and tyrosine. PTZ decreases the brain malate dehydrogenase activity, glutamine and urea in the males, and phenylalanine in the females. Administration of vitamins B1 and B6 24 h before PTZ delays a seizure in female rats only. This desensitization is not observed at short intervals (0.5-2 h) between the vitamins and PTZ administration. With the increasing interval, the pyridoxal kinase (PLK) activity in the female brain decreases, suggesting that the PLK downregulation by vitamins contributes to the desensitization. Delayed effects of vitamins and/or PTZ are mostly gender-specific and interacting. Our findings on the gender differences in sensitivity to epileptogenic factors, action of vitamins B1/B6 and associated biochemical events have medical implications.