Functions of the Liver
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
The liver has an important role in protein catabolism. The rate of protein turnover in the liver is 10 days, which contrasts sharply with the rate of 180 days for muscle proteins. Amino acid degradation is by transamination, deamination and decarboxylation. Oxidative deamination breaks down surplus amino acids and releases energy. Deamination may be coupled with the transfer of an amino group from one amino acid to another (transamination). These reactions produce acetyl CoA, oxoglutarate, succinyl CoA, oxaloacetate and fumarate, all of which enter the citric acid cycle. Amino acids (such as arginine, histidine, lysine, methionine, threonine, phenylalanine and tryptophan) are degraded mainly in the liver, whereas aspartic acid, glutamic acid, glycine, proline and alanine are metabolized in both hepatic and muscle tissue.
Liver physiology
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2015
The liver has an important role in protein catabolism. The rate of protein turnover in the liver is 10 days, which contrasts sharply with the rate of 180 days for muscle proteins. Amino acid degradation is by transamination, deamination and decarboxylation. Oxidative deamination breaks down surplus amino acids and releases energy. Deamination may be coupled with the transfer of an amino group from one amino acid to another (transamination). These reactions produce acetyl CoA, oxoglutarate, succinyl CoA, oxaloacetate and fumarate, all of which enter the citric acid cycle. Amino acids (such as arginine, histidine, lysine, methionine, threonine, phenylalanine and tryptophan) are degraded mainly in the liver, whereas aspartic acid, glutamic acid, glycine, proline and alanine are metabolized in both hepatic and muscle tissue.
Power and power endurance: the explosive sports
Nick Draper, Helen Marshall in Exercise Physiology, 2014
In the section on protein metabolism in Chapter 2 the process of amino acid deamination was described. As a result of deamination the amine, or nitrogen component of an amino acid, is removed. This process enables the remaining part of an amino acid, the α-keto acid, to be metabolised to produce an alternative supply of ATP. In the adenylate deaminase reaction (ADR), with the addition of water, the amine component of AMP is removed to leave inosine monophosphate (IMP) and the amine group which forms ammonia (NH3) (Figure 9.8). The ADR reaction occurs during high-intensity exercise to reduce the buildup of AMP within the sarcoplasm. A high level of AMP would inhibit the adenylate kinase reaction and interfere with sustained ATP production.
Serum and plasma amino acids as markers of prediabetes, insulin resistance, and incident diabetes
Published in Critical Reviews in Clinical Laboratory Sciences, 2018
C. Gar, M. Rottenkolber, C. Prehn, J. Adamski, J. Seissler, A. Lechner
Protein provides the most important structural and functional components of the human body. Muscle protein in particular also serves as an energy store. Protein-derived amino acids are constantly turned over and transported between organs and the blood stream. In anabolic phases, dietary amino acids are added to the body’s protein pool. These phases alternate with catabolic states, which occur with energy deprivation or when dietary protein is available in excess of structural requirements. Then energy is provided by the breakdown of endogenous protein and amino acids can be used for gluconeogenesis [16]. Over-activation of gluconeogenesis occurs in most cases of prediabetes and T2D [17,18]. Glucagon stimulates this process in the liver and, to a lower extent, in the kidneys [16]. After deamination, amino acids form keto acids like acetyl-CoA (derived from leucine, isoleucine, lysine, and tryptophan), alpha-ketoglutarate (derived from glutamate, glutamine, arginine, proline, and histidine), succinyl-CoA (derived from valine), and fumarate (derived from aspartate, asparagine, tyrosine, and phenylalanine), which are further metabolized to oxaloacetate in the Krebs-cycle (Figure 1) [16,19]. Deamination of asparagine and aspartate directly forms oxaloacetate and alanine; the deamination of cysteine, glycine, serine, and tryptophan form pyruvate. Oxaloacetate and pyruvate feed gluconeogenesis [16,19]. Among the amino acids, alanine and glutamine are the most important gluconeogenic precursors in liver (major site of gluconeogenesis) [20–22].
Can we reduce autism-related gastrointestinal and behavior problems by gut microbiota based dietary modulation? A review
Published in Nutritional Neuroscience, 2021
Nalan Hakime Nogay, Marcia Nahikian-Nelms
The catabolism of bacterial amino acids occurs through mechanisms that require deamination or decarboxylation reactions in the human intestine [46]. Protein consumption ensures an increase in all microbial densities. The consumption of animal-derived proteins increases the relative abundance of Bacteroides, Alistipes, Bilophil, and Ruminococcus while decreases that of Bifidobacterium. Plant-derived proteins increase the relative abundance of Bifidobacterium and Lactobacillus and decrease those of Bacteroides and C. perfringens [13]. In a study, the stool samples of 98 individuals were examined to evaluate the effect of diet on the microbiota. Bacteroides was found to have a positive relationship with animal proteins, various amino acids, and saturated fats and a negative relationship with Prevotella, which was associated with high-carbohydrate and simple sugar intake [49].
Role of Heme Iron in the Association Between Red Meat Consumption and Colorectal Cancer
Published in Nutrition and Cancer, 2018
Arianna Sasso, Giovanni Latella
Ammonia is produced by colonic bacteria during amino acid deamination and, to a lesser extent, during urea hydrolysis by bacterial urease (65). Excessive amounts of ammonia, which are found already after a week of supplementation with protein-rich foods, alter cell viability and nucleic acid synthesis and stimulate the growth of cancerous cells in culture (66). Clinton et al. have reported that intrarectal infusion of high concentrations of ammonium acetate significantly increased carcinogenesis and caused loss of mucus in rat colon (67). Various compounds are produced during the degradation of aromatic amino acids (tyrosine, tryptophan, and phenylalanine) by bacteria (68). In particular phenol, the end-product of tyrosine degradation, reacts in vitro with nitrites to produce p-diazoquinone, which possesses mutagenic activity (69).