Bicarbonate and the Pathway of Glutamate Oxidation in Isolated Rat‐Liver Mitochondria

Abstract

1. The factors affecting the pathway of glutamate oxidation were studied in isolated rat-liver mitochondria in incubations of 2-3 min.2. It was found that bicarbonate at a physiological concentration has a profound effect on the pathway of glutamate oxidation. Ammonia formation via glutamate dehydrogenase is stimulated by bicarbonate [from 5.48 0.73 (n = 8) nmol . min-' . mg protein-'], whereas aspartate formation via the transamination pathway is inhibited [from 38.41 5 2.24 (n = 9) to 24.56 3.28 (n = 6) nmol . min-l . mg protein-' 3.0.29 (n = 10) to 9.57 3. Bicarbonate has no effect on the rate of transport of glutamate via the glutamate-hydroxyl translocator. 4. The interaction of bicarbonate with the pathway of glutamate oxidation occurs primarily at the level of succinate dehydrogenase, due to competitive inhibition of the enzyme by bicarbonate.5. Inhibition by bicarbonate of the transamination pathway leads to a decrease in intramitochondrial 2-oxoglutarate, so that the deamination pathway is stimulated.6. Using an equation which describes flux through glutamate dehydrogenase kinetically, it could be shown that the bicarbonate-induced decrease in intramitochondrial2-oxoglutarate quantitatively accounts for the enhanced rate of deamination.7. It is concluded that in the intact liver flux through glutamate dehydrogenase is sufficient to account for the ammonia formation required for urea synthesis from substrates such as alanine.

Key Process Conditions for Production of C 4 Dicarboxylic Acids in Bioreactor Batch Cultures of an Engineered Saccharomyces cerevisiae Strain

“…Intriguingly, succinate dehydrogenase, which catalyzes the oxidation of succinate to fumarate in the tricarboxylic acid (TCA) cycle, has been shown to be inhibited by bicarbonate in several organisms (7,15,49). This inhibition could limit the (re)oxidation of succinate to malate, thereby explaining the observed effect of CO 2 on the production of succinate and malate.…”

The malate/aspartate shuttle and pyruvate kinase as targets involved in the stimulation of gluconeogenesis by phenylephrine

“…Glucose and lactate were measured spectrophotometrically by standard enzymic procedures [17]; pyruvate was measured either spectrophotometrically or fluorimetrically ; glutamate and dihydroxyacetone phosphate were measured fluorimetrically [ 171 ; 2-oxoglutarate was measured fluorimetrically as described by Wanders et al [18]; cyclic AMP was measured as described by Tovey et al [19].…”

Phosphoenolpyruvate Carboxykinase as the Sole Anaplerotic Enzyme in Saccharomyces cerevisiae

“…The multiple dependencies for growth on glucose exhibited by the evolved Pyc Ϫ PEPCK-expressing S. cerevisiae strains (requirements for CO 2 enrichment, for PEPCK overexpression, and for a lowered pyruvate kinase activity) can be explained only if anaplerosis occurred via PEPCK. The absence of glyoxylate cycle derepression mutants during selection might be explained by inhibition of succinate dehydrogenase by CO 2 (4,15,40). As this enzyme is required for a functional glyoxylate cycle, its inhibition by CO 2 would represent a second hurdle in addition to the glucose repression of the glyoxylate cycle enzymes isocitrate lyase and malate synthase (16,17,20,32).…”