Lower-intensity aerobic endurance sports
Nick Draper, Helen Marshall in Exercise Physiology, 2014
The Krebs cycle, also known as the tricarboxylic acid cycle or citric acid cycle, involves nine reactions which occur within the matrix of the mitochondria (see Figure 12.3). Through their respective primary metabolic pathways, carbohydrates and fats are converted to acetyl CoA for entry to the Krebs cycle. Protein, if catabolised for energy production, enters the Krebs cycle at a variety of points according to the structure of its carbon-based skeleton. These entry points for protein are shown in Table 12.1. The Krebs cycle, shown in Figure 12.8, was named after Sir Hans Krebs who first identified the nine reactions in the pathway. This process, as with glycolysis and β oxidation, releases hydrogen atoms for use within the electron transport chain. The Krebs cycle employs both FAD and NAD+ as co-enzyme carriers for the hydrogen atoms removed from substrates. In Figure 12.8 both the reactions and the chemical compositions of the intermediary substrates within the Krebs cycle are illustrated.
Diseases of the Nervous System
George Feuer, Felix A. de la Iglesia in Molecular Biochemistry of Human Disease, 2020
The brain has an absolute dependence on the oxidation of carbohydrates. Lack of glucose by any means will depress cerebral metabolism and consequently affecting function. Insulininduced hypoglycemia can also reduce brain metabolism. The effect is reversible if the hypoglycemia is of short duration and not excessive. There are differences in the events occurring during ischemia and hypoglycemia. During hypoglycemia, metabolic changes are different from those in circulatory failure, and the onset of functional and metabolic changes is slow. The tricarboxylic acid cycle is functioning and the concentration of endogenous substrates is enough to maintain energy metabolism for 20 to 25 min. Hypoglycemia may occur in the brain associated with liver disease, insulin-secreting tumors, and insulin overdose. The clinical signs of hypoglycemia, such as increased perspiration and tachycardia, are due to the release of large amounts of epinephrine. Drowsiness and confusion are apparent when blood glucose is reduced to 30 mg/dl, and coma ensues at 20 mg/dl. Below this level there is loss of neurons. Prolonged hypoglycemia can produce permanent damage, mental and psychological disorders, and death. Infantile hypoglycemia is found to be a significant cause of neonatal brain damage.
Ageing, Neurodegeneration and Alzheimer's Disease
James N. Cobley, Gareth W. Davison in Oxidative Eustress in Exercise Physiology, 2022
Mitochondria are critical in the production of ATP as they are the site for oxidative phosphorylation. The oxidation of NADH and FADH2, formed in glycolysis, fatty acid oxidation and the tricarboxylic acid cycle (TCA), is used to reduce ground state molecular dioxygen to water in the electron transport chain (ETC) which traverses the inner mitochondrial membrane (Zhao et al., 2019). During this process, protons are pumped into the intramembrane space to create a pH gradient and mitochondrial membrane potential (Belenguer et al., 2019), termed the proton-motive force (Mitchell, 1966). The entry of protons back into the matrix via the ATPase enzyme enables the phosphorylation of ADP to synthesis ATP (Belenguer et al., 2019). Mitochondrial oxidative phosphorylation accounts for a large portion of ATP synthesis in the brain, and therefore, a sufficient supply of metabolites is critical for effective cellular respiration. Although predominantly associated with their role in generating ATP, mitochondria are also involved in a number of other critical cellular processes, which include programmed cell death, calcium signalling, fatty acid oxidation and the innate immune response (Scott and Youle, 2010). Therefore, the development of mitochondrial dysfunction in an ageing brain would pose a significant challenge to cell function.
The ancestral stringent response potentiator, DksA has been adapted throughout Salmonella evolution to orchestrate the expression of metabolic, motility, and virulence pathways
Published in Gut Microbes, 2022
Helit Cohen, Boaz Adani, Emiliano Cohen, Bar Piscon, Shalhevet Azriel, Prerak Desai, Heike Bähre, Michael McClelland, Galia Rahav, Ohad Gal-Mor
Some Enterobacteriaceae species, including S. enterica, are capable of utilizing citrate as a carbon and energy source. Under aerobic conditions, growth on citrate is dependent on an appropriate transport system and a functional tricarboxylic acid (TCA cycle, also known as Krebs or citric acid cycle). Citrate fermentation requires the functional citrate transporter CitT, the citrate lyase (encoded by citCDEFXG), and the two-component regulatory system encoded by citAB.29 RNA-Seq data showed that DksA strongly represses the citrate regulon in S. Typhimurium and also (although to a lesser extent) in S. bongori and E. coli (Figure 3(a)). qRT-PCR analysis confirmed these results and showed that in S. Typhimurium, in the absence of DksA, the expression of citC, citD and citX increased by 6, 2.5, and 3-fold, respectively (Figure 3(b)), indicating that DksA is a negative regulator of the citrate regulon in S. enterica.
Carboxylic acids accelerate acidic environment-mediated nanoceria dissolution
Published in Nanotoxicology, 2019
Robert A. Yokel, Matthew L. Hancock, Eric A. Grulke, Jason M. Unrine, Alan K. Dozier, Uschi M. Graham
The carboxylic acids that accelerate nanoceria dissolution are biologically relevant. Lactic acid is a product of anaerobic glycolysis and anaerobic metabolism. Citric, malic, and succinic acids are intermediates in the tricarboxylic acid cycle. Acetic acid is a product of free fatty acid and alcohol metabolism. The presence and concentration of these small carboxylic acids in conjunction with an acidic pH may influence nanoceria dissolution and stabilization of the released cerium ion in vivo. Although the concentration of most of these carboxylic acids in mammalian cells has apparently not been determined, the interstitial fluid total organic anion concentration is ∼5 mEq/l, citric acid can reach 10 mM in some cells, and muscle lactate can reach ∼30 mM during intense exercise (Legiša and Kidrič 1989; Bangsbo et al. 1990). Their constant turnover provides a continual source of carboxylic acids to form complexes with nanoceria in vivo. Citric, succinic, malic, acetic, and other carboxylic acids are released by plant roots to chelate and acquire minerals (Cieslinski et al. 1997), can increase soil acidity, enhance nanoceria dissolution, and perhaps cerium uptake (Zhang et al. 2017).
Metformin mitigates impaired testicular lactate transport/utilisation and improves sexual behaviour in streptozotocin-induced diabetic rats
Published in Archives of Physiology and Biochemistry, 2021
Victor Udo Nna, Ainul Bahiyah Abu Bakar, Azlina Ahmad, Mahaneem Mohamed
Lactate dehydrogenase catalyses the interconversion of pyruvate (formed as a result of glycolysis) to lactate. When formed, pyruvate can either be: (i) interconverted to alanine by alanine transaminase, (ii) interconverted to lactate by LDH, or (iii) transferred into tricarboxylic acid cycle (Yang et al.2002, Alves et al.2013b). Increased intra-testicular LDH activity and lactate level in DC group in the present study suggests that the interconversion of pyruvate to lactate was prioritised among the three possible endpoints of pyruvate mentioned above, in a bid to up-regulate lactate production. Also, increased LDH activity in DC group may be a negative feedback targeted at producing more lactate since lactate transporters (MCTs) and LDHc were down-regulated. Interestingly, treatment with metformin decreased intra-testicular glucose and lactate levels, leading us to suggest that testicular GCs utilisation of lactate may be responsible for the decreased intra-testicular lactate levels. This is so because regardless of the up-regulation of GLUT3 mRNA transcript level, glucose level decreased, and LDH activity also decreased following treatment with metformin.
Related Knowledge Centers
- Anaerobic Respiration
- Cellular Respiration
- Chemical Reaction
- Fermentation
- Precursor
- Protein
- Carbohydrate
- Redox
- Acetyl-Coa
- Fat