Author: Katherine Marie Kennedy

Publisher:

Published: 2014

Total Pages:

ISBN-13: 9781321363029

The use of assumptions lies at the base of every experiment and project conducted, regardless if theoretical, mathematical, or experimental. Those assumptions must be as accurate as possible to ensure the accuracy of the project and/or theory. This thesis revises and analyzes the assumptions used in describing energy and protein metabolism, particularly the ATP values associated with the reducing equivalents that are generated through oxidative phosphorylation and the effect those new values of ATP on a variety of energy producing/consuming metabolic pathways in ruminants and non-ruminants. Much of energetics relies on the electron transport chain and ATP synthase, arguably, the most important structures in mammalian cells as a result of its combined capacity for mass production of ATP through oxidation phosphorylation. Over the decades, progress has been made in the determination of the mechanism of each of the five complexes (NADH-ubiquinone oxidoreductase (Complex I), succinate-ubiquinone oxidoreductase (Complex II), cytochrome bc1 complex (Complex III), cytochrome c oxidase (Complex IV), and ATP synthase (Complex V)) and in the determination of the proton pumping stoichiometry associated with complex I, III, and IV. The finding that bovine heart ATP synthase requires the flow of 8 protons from the intermitochondrial membrane space into the mitochondrial matrix through the ATP synthase to produce 3 ATP is one of the most notable of these discoveries. This information, as well as advances in biochemical research, enables the calculation of the values of ATP associated with the reducing equivalents NADH, flavin adenine dinucleotide (FADH2), and guanosine triphosphate (GTP). Those advances include the identification of the costs of: (1) the malate-aspartate shuttle for transporting protons and electrons into the mitochondria, (2) pyruvate transport into the mitochondria, and (3) counter transport of ATP and GTP out of the mitochondria with the concomitant costs of transporting ADP, GDP, and inorganic phosphorous into the mitochondria. As currently accepted, electron transport results in 10 and 6 protons pumped from the matrix to the intermitochondrial space when the electrons are derived from NADH + H+ and FADH2, respectively. Consequently, when each is coupled to oxidative phosphorylation 2.7 ATP are produced from each NADH + H+ formed in the mitochondria, 2.5 ATP from each NADH + H+ formed in the cytosol, and 1.6 ATP from each mitochondrial FADH2. Mitochondrial GTP formed in the TCA cycle is equivalent to 0.7 ATP when GTP is transported out of the mitochondria. These assumptions were then applied to energetics, including the energy associated with AA oxidation. Other key aspects in working with energetics and protein metabolism include establishing values for the following three assumptions: (1) the average molecular weight (MW) of an AA; (2) the percent nitrogen (%N) content of the protein; and (3) the ATP cost associated with the formation of one peptide bond. Assuming that the average MW of an AA is 110 g/mol for a protein is a reasonable assumption when considering the whole organism, but individual tissues may differ. Additionally, although the assumption that livestock muscle products have a %N value of approximately 16% is reasonable, the determination of the %N content based on the AA analysis of the product is best. For decades, the cost of 5 ATP per peptide bond synthesized has been an underlying assumption; however, this research suggests that the cost of synthesizing a peptide bond is 4.1 ATP. Overall, the efficiency of capturing chemical energy as ATP from oxidative processes is decreased when recent research findings are applied to theoretical calculations in both ruminant and non-ruminant animals.