Fatty acids β-oxidation process.

. The processcan be divided into three stages: β, transfer, and oxidation.. 1. Fatty acids arelike glucose, fatty acids are also active before metabolism. Its active form is thioester: fattycoA, the enzyme that catalytic fatty acids is the lipid CoA synthase (acyl CoA synthetase).the polarity of the lipidCoA produced after the inactiveization is enhanced and soluble in water, the molecules have high-energy bonds, the properties are lively, is the specific substrate of the enzyme, and the enzyme affinity is large, so it is easier to participate in the reaction.coA synthase, also known as sulfur
kinase
, is distributed in cytosal plasma, mitochondrial membranes and endosome membranes. Sulfur kinases in cytosal plasma catalyzedshort- and medium-chain fatty acids, enzymes on endosometrys in active long-chain fatty acids, produced lipidCoA, and then entered the endosome mesh for triglyceride synthesis; and enzyme-active long-chain lipid CoA on mitochondrial membranes entered the mitochondrials into β-oxidation.. 2. LipidCoA into mitochondrials: catalytic fatty acids β-oxidation of the enzyme line mitochondrial substation, but long-chain lipid CoA can not freely pass through the mitochondrial membrane, to enter the mitochondrial substate needs carrier transport, this carrier is carnitine, that is, 3-hydroxy-4-triaminobutyric acid.
long-chain fatty coA and carnitine reactions to produce coenzyme A and lipid carnitine, and the 3 hydroxyls of fatty base and carnitine are connected by ester bonds.the enzyme that catalyzes this reaction is carnitine acyl transferase
carnitine
metastase. This enzyme is found on both sides of the membrane inside and outside the mitochondrial, and isoenzyme, called carnitine lipid transferase I and carnitine lipid transferase II. Enzyme I. Transforms the lipid CoA
cell
into coenzyme A and fatty carnitine, which enter the mitochondrial membrane. Enzyme II, located on the inside of the membrane of the mitochondrial body, converts fatty carnitine into carnitine and lipid CoA, carnitine re-functions as a carrier, and liccoline CoA enters the mitochondrial substrate and becomes the base of the fatty acid β-
oxidase
system (Figure 5-10).
5-10 Carnitine is involved in the transfer of lipid coenzyme A into mitochondrial schematics . Enzyme I.: Carnitine lipid transferase ase II. located on the inside of the membrane in mitochondrial body The speed at which long-chain lipid CoA enters the mitochondrial is regulated by carnitine lipid transferase I. and enzyme II., enzyme I. inhibited by acetyl CoA, and enzyme II. inhibited by insulin. Acrylic CoA is the raw material for the synthesis of fatty acids, and insulin inhibits enzyme I. by inducing the synthesis of acetylCoA pyrethylase to increase the concentration of acetylCoA. It can be seen that insulin has indirect or direct inhibitory effects on carnitine lipid transfer enzymes I. and enzyme II. Insulin secretion decreases during hunger or fasting, carnitine lipid transferase I. and enzyme II. Activity increases, and long-chain fatty acids are transferred into mitochondrial oxidation for energy supply.. 3.β-Oxidation reaction process: The entry into the β oxidation of the lipidCoA mitochondrial substation is subject to a four-step reaction, i.e. dehydrogenation, watering, rehydrogenation and sulfur dehydration, resulting in a molecule of acetylCoA and a new lipidCoA with two less carbons.first step dehydrogenation reaction is active by lipid CoA
dehydrogenase
, supplemented by FAD, and lipid CoA strips one hydrogen atom on α and β carbon atoms each to produce trans-double-bonded α, β-ole fatty coenzyme A.second step of the watering reaction is catalyzed by acrylCoA hydrase, which produces an L-formed β-hydroxyl CoA.the third step of dehydrogenation is to produce β-hydroxyladylCoA dehydrogenation to produce β ketone lipid CoA under the catalysis of β-hydroxyladylCoA decodase (coenzyme is NAD plus).step four thiolysis reaction is catalyzed by β-ketone sulfatease, β-ketone estercoA breaks the chain between α and β carbon atoms, plus a molecule of coenzyme A to produce acetylCoA and a lipidCoA with two less carbon atoms.The above four-step reaction is similar to the process of producing oxalic acid from amber acid through yanhusoic acid and apple acid in the TCA cycle, but the fourth step of β-oxidation is sulfuric acid, and the next reaction of oxalacetic acid is to shrink with acetylCoA to produce citric acid. long-chain lipid CoA through the above cycle, the carbon chain reduces two carbon atoms, the production of a molecule acetylCoA, repeated the above cycle, will gradually produce acetylCoA. can be seen from the above, the β-oxidation process of fatty acids has the following characteristics. The first step is to active fatty acids to produce lipidCoA, which is an energy-consuming process. Medium and short-chain fatty acids do not need carriers to be pulled straight into mitochondrials, while long-chain lipid coA requires carnitine transport. β-oxidation reaction is carried out in the mitochondrial body, so red blood cells without mitochondrials cannot oxidize fatty acids for energy supply. β-oxidation process is generated by FADH2 and NADH plus H, which are transmitted through the respiratory chain to oxygen to produce water, require oxygen participation, and oxidation of acetylCoA requires oxygen. Therefore, β-oxidation is an absolute oxygen demand process. process of β-oxidation of fatty acids can be shown in the figure below (Figure 5-11): Figure 5-11 fatty acids β oxidation reaction process

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