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Bioenergetics
Published in Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan, Strength and Conditioning in Sports, 2023
Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan
Beta-oxidation is a process of extracting energy from FFA. Beta-oxidation is primarily a function of the mitochondrial trifunctional protein. The MTFP is an enzyme complex associated with the inner mitochondrial membrane, although especially long-chain FA are oxidized in oxidative organelles, the peroxisomes. The peroxisomes use a similar oxidative enzyme group as found in the inner mitochondrial membrane. Free fatty acids undergoing β-oxidation result in the accumulation of acetyl-CoA, and H+. The acetyl-CoA can enter the Krebs cycle and the protons, which are carried to the ETS by nicotinic adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD), can enter the electron transport system (ETS) (see Figure 2.5). Type I muscle fibers generally contain high concentrations of oxidative enzymes compared to type II, thus the process of FFA oxidation is quite important for these fibers (35, 79). Fat use during exercise becomes increasingly important with duration (108).
Metabolic Cardiology
Published in Stephen T. Sinatra, Mark C. Houston, Nutritional and Integrative Strategies in Cardiovascular Medicine, 2022
The principal role of carnitine is to facilitate the transport of fatty acids across the inner mitochondrial membrane to initiate beta-oxidation. The inner mitochondrial membrane is normally impermeable to activated coenzyme A (Co A) esters. To affect transfer of the extracellular metabolic byproduct acyl-Co A across the cellular membrane, the mitochondria deliver its acyl unit to the carnitine residing in the inner mitochondrial membrane. Carnitine (as acetyl-carnitine) then transports the metabolic fragment across the membrane and delivers it to coenzyme A residing inside the mitochondria. This process of acetyl transfer is known as the carnitine shuttle, and the shuttle also works in reverse to remove excess acetyl units from the inner mitochondria for disposal. Excess acetyl units that accumulate inside the mitochondria disturb the metabolic burning of fatty acids.
Energy Provision, Fuel Use and Regulation of Skeletal Muscle Metabolism During The Exercise Intensity/Duration Continuum
Published in Peter M. Tiidus, Rebecca E. K. MacPherson, Paul J. LeBlanc, Andrea R. Josse, The Routledge Handbook on Biochemistry of Exercise, 2020
Once inside the mitochondria, fat enters the beta-oxidation pathway with the formation of acetyl-CoA and reducing equivalents (NADH, FADH2), and the long-chain nature of FFA results in the production of large amounts of aerobic ATP (Table 2.1). Interestingly, there has been no concrete evidence that there is metabolic regulation in the beta-oxidation pathway—it simply responds to the provision of substrate (75). Given that the beta-oxidation pathway exists in the mitochondria, the mitochondrial volume of the muscle cell determines the overall capacity to oxidize fat during exercise (39, 66).
Radiation metabolomics in the quest of cardiotoxicity biomarkers: the review
Published in International Journal of Radiation Biology, 2020
Michalina Gramatyka, Maria Sokół
The heart, as an organ with very high energy demands, is particularly vulnerable to mitochondrial dysfunction. Mitochondria occupy approximately 40% of the cardiomyocytes volumes, and cardiomyocytes constitute about 75% of the cells in the heart (Barjaktarovic et al. 2011; Sridharan et al. 2014). This allows the heart to produce enough ATP to cover its energy demands. In the heart the processes of beta oxidation of fatty acids provide 60–80% of the produced energy (Constantinou et al. 2007). Glucose, ketone bodies, succinate, lactate, amino acids and proteins also may serve as a fuel for ATP production (Drake et al. 2012; Tapio 2017), although they are less energetically efficient than fatty acids (Ussher et al. 2016). It is reported that cardiac exposure to low doses of radiation shifts the balance of energy production from beta oxidation toward other processes, like glycolysis (Tapio 2017).
Nutritional Supplementation: A Case for L-Carnitine
Published in Journal of Dietary Supplements, 2019
L-carnitine is a conditionally essential amino acid primarily found in ruminants (i.e., beef and milk products). It is synthesized de novo from L-lysine and L-methionine primarily in the liver and kidneys (Marcovina et al., 2013). Patients with underlying liver disease (nonalcoholic fatty liver disease from obesity) or kidney disease (diabetic or hypertensive nephropathy) may not produce adequate levels (Marcovina et al., 2013). Intracellularly, L-carnitine works to transport fatty acids from the cytoplasm to the mitochondria for beta oxidation and energy metabolism. In addition, supplementation in animal models has shown beneficial effects on endothelial nitric oxide synthetase (eNOS) levels by reducing mitochondrial oxidative stress, thereby promoting endothelial function (Marcovina et al., 2013). Specific to human trials, a growing body of evidence indicates a potential benefit of L-carnitine supplementation in the treatment of coronary artery disease, metabolic syndrome, and obesity.
Ophthalmic manifestations of Heimler syndrome due to PEX6 mutations
Published in Ophthalmic Genetics, 2018
Nutsuchar Wangtiraumnuay, Waleed Abed Alnabi, Mai Tsukikawa, Avrey Thau, Jenina Capasso, Reuven Sharony, Chris F. Inglehearn, Alex V. Levin
The peroxisome is a cytoplasmic organelle. Its main function is the breakdown of very long chain fatty acids through beta-oxidation. The PEX1 and PEX6 proteins bind with adenosine triphosphate (ATP) to form a heterohexameric ATPase which is associated with various cellular activities that fuel essential protein transport across peroxisomal membranes, the final steps of peroxisomal matrix-protein import (19–23). PEX1 and PEX6 are expressed in the retina, especially in photoreceptors (24). Abnormal PEX6 and PEX1 proteins result in abnormal peroxisomal function, leading to the accumulation of very long chain fatty acids. Histopathology of other peroxisomal disorders shows accumulation of characteristic bileaflet fatty acid inclusions in photoreceptors, RPE and pigment laden macrophages (13). Fatty acid accumulation may create the lipofuscin-like substances which appear as hyperfluorescent flecks seen on FAF in our patients.