The BCKAD is generally in the inactivated phosphorylated form and activated by a protein phosphatase after ingestion of the branched chain amino acids. The 20 amino acids commonly found in animals are alanine alanine, organic compound, one of the 20 amino acids commonly found in animal proteins. Lysine and leucine are the only two amino acids that produce Acetyl CoA or Acetoacetyl CoA without any glucogenic byproducts. A summary of the catabolism of amino acids through the TCA cycle is shown in Fig. Ketogenic amino acids are alpha and beta keto acids that are broken down into ketone bodies and cannot be used for gluconeogenesis. The next two steps are catalyzed by isocitrate dehydrogenase. Ketogenic amino acids are the class of amino acids that produce acetyl CoA and acetoacetyl CoA during the catabolism of the amino acid. The third aromatic amino acid, tryptophan, is converted to acetoacetate as shown in Fig. These are not the amino acids that will derive energy from your body's pre-existing fat stores. The 90% of these water-soluble fuels undergo terminal oxidation, primarily by the brain and muscle. While the great majority of ketone bodies are synthesized from the acetyl CoA that is derived from the β-oxidation of fatty acids in the mitochondria, a small quantity can be synthesized from ketogenic amino acids during starvation. Since β-OHB− and AcAc− are excreted with near equimolar quantities of NH4+, ketosis is an energetically cheap way to excrete nitrogen (the synthesis of urea requires four molecules of ATP per molecule of urea). Ketogenic amino acids form acetoacetate or acetyl CoA. Finally, for each gram of nitrogen lost in the urine 3.57 g of glucose is synthesized. Over this period, the average resting human oxidizes a minimum of 3 g of fat per kg FFM per day. If BCKAD is mutated (poorly or not expressed), branched chain amino acids accumulate in the blood and urine. Serine dehydratase converts serine to pyruvate as shown in Fig. Hexoses, glycerol, fatty acids, and amino acids render acetyl-CoA, which is oxidized in the citric acid cycle. For example, the degradation of phenylalanine starts with phenylalanine 4-monooxygenase, which adds a hydroxyl group to phenylalanine to produce tyrosine. Triacylglycerols in adipose tissue are hydrolyzed by lipase, a hormone-regulated enzyme. However, the essentiality of n-3 fatty acids in humans was first demonstrated only in the early 1980s (Holman et al., 1982). Most of the remainder is excreted in the urine. Those amino acids that do not enter the TCA cycle are either ketogenic (form fatty acids) or glucogenic (form glucose). Biotin can also be synthesized by bacteria in the colon. Amino acids that contain three carbon atoms, such as alanine, serine, glycine (via serine), and cysteine, are converted into pyruvate, (the entry point for the citric acid cycle or gluconeogenesis). The standard amino acids are characterized by different carbon skeletons, so their conversions to citric acid cycle intermediates often involve transamination with glycolytic or tricarboxylic acid cycle (TCA) cycle intermediates [7–9]. Glycogenolysis is regulated through the control of glycogen phosphorylase and phosphorylase kinase. furthermore, this is in contrast to the glucogenic amino acids, which are converted into glucose. SAM methylase converts SAM to S-adenosylhomocysteine and then to homocysteine. Metabolism of some amino acids may lead to the formation of more than one of the above-listed metabolic intermediates and these amino acids belong to both categories: glucogenic and ketogenic. As early as the1930s, the essentiality of linoleic acid (18:2 n-6) and alpha-linolenic acid (18:3 n-3) in rat diets was identified (Burr and Burr, 1930). The carbon skeletons are converted into pyruvate, 2-oxoglutarate, succinyl-CoA, fumarate, and oxaloacetate and they act as glucose precursors. The liver not only stores glucose as glycogen, but also converts fuels such as FFA, amino acids, lactate, pyruvate, and glycerol to glucose and ketone bodies and detoxifies the ammonia, which is produced from the deamination of amino acids, by converting it to urea. Here, we found that a … Subsequently, isovaleryl-CoA is dehydrogenated to form β-methylcrotonyl-CoA by the enzyme isovaleryl-CoA dehydrogenase. Taking an essential amino acid supplement (which includes the ketogenic amino acids lysine and leucine) can help protect against any protein insufficiencies you may encounter while following dietary restrictions, such as the high-fat, moderate-protein requirements of the keto diet. 13.37). Leucine degradation is similar to the branched amino acids valine and isoleucine (see below). Amino acids that are metabolized to pyruvate are alanine, cysteine, and serine. The degradation of alpha and beta-amino acids produces acetyl-CoA or acetoacetate and other ketone bodies. Life has helped me regain my energy and my muscles. The formimino group is then transferred by glutamate formiminotransferase to tetrahydrofolate to produce glutamate and N5-formimino-tetrahydrofolate [4]. Kamel S. Kamel MD, FRCPC, Mitchell L. Halperin MD, FRCPC, in Fluid, Electrolyte and Acid-Base Physiology (Fifth Edition), 2017. Practice: Collagen mutations result … The carbon skeletons are catabolized to acetyl-CoA or acetoacetate and can therefore lead to production of fatty acids or ketone bodies. During the postabsorptive period and starvation, serum fatty acid levels increase and serum ketone bodies are also increased. Histidine is converted into urocanate by a deamination reaction catalyzed by the enzyme histidine ammonia lyase. In the case of methionine, it is first converted to S-adenosylmethionine (SAM) by methionine adenosyltransferase. Together with CoASH and NAD+, branched chain α-keto acid dehydrogenase (BCKAD) converts the keto acids to the corresponding CoA derivatives. The first step is fusion of the acetyl group of acetyl-CoA with oxaloacetate, catalyzed by citrate synthase. ketogenic amino acid: [-jen′ik] an amino acid whose carbon skeleton serves as a precursor for ketone bodies. Want to know more about amino acids and how supplementation can improve your health? Catabolism of amino acids through the citric acid cycle. With so many high-yield proteins, any dietary practice—be it vegetarian, vegan, kosher, or allergy-restrictive—can still gain you the essential amino acids for perfecting your ketogenic journey if you're diligent about ensuring your protein macros. ! Some ketogenic amino acids, such as leucine, lysine, tryptophan, alanine, and tyrosine can be oxidized to generate acetyl-CoA for ketone body synthesis. Methionine, valine, and isoleucine are catabolized into propoinyl-CoA that is converted into d-methylmalonyl-CoA by propionyl-CoA carboxylase via fatty acids β-oxidation. Glucose also produces α-ketoacids. Better yet, know what basic foods have the ketogenic keys to turn fatty acids into ketone bodies. Lysine and leucine are the only two amino acids that produce Acetyl CoA or Acetoacetyl CoA without any glucogenic byproducts. Threonine dehydrogenase (NAD+ coenzyme) converts threonine to α-amino-β-ketobutyrate, and α-amino-β-ketobutyrate lyase converts it to acetyl CoA plus l-glycine (Fig. The demonstration that β-OHB− and AcAc− could serve as major fuels for the metabolism of the brain during starvation was a critical factor in evaluating the roles of fatty acid oxidation, amino acid mobilization, glucose conservation, and urinary nitrogen excretion during prolonged starvation. Allosteric regulation of phosphofructokinase is responsible for this effect. Transamination enzymes that catalyze key reactions require a pyridoxal phosphate cofactor [6, 10]. Ketogenic amino acids form acetoacetate or acetyl CoA. Marc Yudkoff. β-Methylglutaconyl-CoA is then hydrated by β-methylglutaconyl-CoA hydratase to form β-hydroxy-β-methylglutaryl-CoA that is then cleaved into acetyl-CoA and acetoacetate. For example, isoleucine catabolism produces both acetyl-CoA, which makes it a ketogenic amino acid, and succinyl-CoA, which leads to glucose production [7–9]. Histidine can form glutamate through the pathway: l-Histidine (deamination by histidine ammonia lyase) → urocanate (addition of H2O by urocanate hydratase) → 4-imidazolone 5-propionate (hydrolysis by imidazole propionase) → N-formininoglutamate (+ tetrahydrofolate) → glutamate+N5-formimino-tetrahydrofolate (by glutamate formiminotransferase) and glutamate can be converted to α-ketoglutarate by aspartate aminotransferase (above, reverse reaction). Branched chain α-ketoacid dehydrogenase is a multienzymatic complex similar to pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase. Glycolysis is controlled by targeting hexokinase and phosphofructokinase. In this section, we explain how each single amino acid is catabolized. Citrate is isomerized by dehydration and rehydration to isocitrate. As fasting is prolonged, the kidney cortex also contributes to fuel homeostasis by conserving substrates and sharing the gluconeogenic role with the liver. Hanson, in Encyclopedia of Biological Chemistry (Second Edition), 2013. It's better to know how to read the nutrition label with a keen (keto) eye. Hexoses, glycerol, fatty acids, and amino acids render acetyl-CoA, which is oxidized in the citric acid cycle. Acetone and CO2 are formed from the nonenzymatic degeneration of AcAc−. Thus, a large, but not obese adult man, weighing 80 kg, with a body composition of 80% FFM (64 kg) and 20% fat mass (16 kg) oxidizes a minimum of 192 g of fat per day. The enzyme aconitase catalyzes these two steps using cis-aconitate as the intermediate. The reactions involving the other amino acids, as discussed above, take place mainly in the liver. Cysteine also can be converted to pyruvate, and the three alkyl carbons of tryptophan are converted to alanine, and then alanine aminotransferase converts the alanine to pyruvate. Also, these products can further convert into ketone bodies. Branched chain α-ketoacid dehydrogenase is phosphorylated by a kinase, which inactivates the enzyme similarly to the phosphorglation dependent mechanism of pyruvate dehydrogenase inhibition [5]. There are few synthetic processes that are quantitatively as large as the daily rate of ketogenesis during starvation. Alanine is converted into pyruvate by a reaction catalyzed by the enzyme alanine aminotransferase, which reversibly transfers the amino group from the amino acid alanine to 2-oxoglutarate to produce pyruvate and glutamate. Looks like your cart is empty! The citric acid cycle is regulated at various levels, including citrate synthase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and glutamate dehydrogenase. Eventually, the enzyme homogentisate 1,2-dioxygenase catalyzes the formation of 4-maleylacetoacetate, which is converted into 4-fumarylacetoacetate by maleylacetoacetate isomerase. The glucose-pyruvate pathway on the left represents glycolysis and gluconeogenesis. Email. Lysine and leucine are solely ketogenic, and leucine is converted to α-ketoisocaproate by transamination, and this is converted to isovaleryl CoA by BCKAD in an oxidative decarboxylation reaction. These are the intermediate products of their catabolism. Figure 5. The building blocks of protein, amino acids can be categorized as exclusively ketogenic, exclusively glucogenic, or like Dr. Jekyll and Mr. Hyde: radically both. The aromatic amino acids, phenylalanine and tyrosine, are degraded to homogentisic acid, then to maleylacetoacetic acid and finally to CO2 and H2O as shown in Fig. Serine hydroxymethyltransferase is able to convert glycine to pyruvate by first converting glycine to serine (shown above). These products are not intended to diagnose, treat, cure or prevent any disease. Ketone bodies are the only fuels synthesized in the body that do not recycle. Another molecule of acetyl CoA is joined by β-hydroxy-β-methylglutaryl CoA (HMG CoA) synthase to form HMG CoA, also generating a hydronium ion (H+). These ketone bodies will then provide energy from your fat stores, without adding carbohydrates, and without impacting insulin or blood sugar levels. Oxidative decarboxylation of pyruvate is modulated via the pyruvate dehydrogenase (PDH) multienzyme complex. To access citrate synthase, the catalyst of this cycle, without glucose or carbohydrates is the value of ketogenic amino acids: it's like buying the product you need without bringing home any unnecessary or harmful packaging around it. AcAc− is then reduced to β-OHB− by β-hydroxybutyrate dehydrogenase. Thus, if 10–12 g of ketone bodies were excreted in the urine, only 5–6 g of the carbon skeleton would be derived from stored triglycerides. Some metabolites (glucose-6-P, pyruvate, acetyl-CoA) are “crossroads” compounds of several metabolic pathways. By continuing you agree to the use of cookies. Beginners at dieting often attempt to lose weight with short-term crash diets, which put the body in starvation mode and cause it to stockpile more fat as soon as possible (an evolutionary protection against times of famine). Succinate thiokinase converts succinyl-CoA to succinate, while first generating ATP/GTP by substrate-level phosphorylation. The brain removes β-OHB− and AcAc− in a concentration-dependent manner. Keto Lemon Recipes to Kick Off the New Year. Branched chain amino acids are catabolized by muscle, adipose, kidney, and brain but not by the liver. The mnemonic story of the citric acid cycle. 13.40. Glutamate is converted to α-ketoglutarate by aspartate aminotransferase (see above, reverse reaction). Because it is bound to protein, its bioavailability varies among the different sources, as it must be released from the protein to be available. Glutamine is converted into glutamate by a reaction catalyzed by the enzyme glutaminase. evidenced elevated levels of 3-hydroxybutyrate, Omega-3 Fatty Acids and Early Life Nutritional Programming, Bioactive Food as Dietary Interventions for Liver and Gastrointestinal Disease, from simple precursors such as glucose or, Comprehensive Biotechnology (Second Edition), Liver Physiology: Metabolism and Detoxification. The citric acid cycle utilizes mitochondrial enzymes for final oxidation of carbohydrates, proteins, and fats. Oxidation pathway starts with the elimination of the amino group with the transaminase; then this group will be fed into the urea cycle. Ketogenic.com; Global Virtual Keto Summit; Keto Awards; Contact Us; Education Amino Acid Catabolism: All amino acids are classified as ketogenic, glucogenic, or both based on what molecules they can be broken down into during their catabolism. Thus, two fatty acids having their first double bonds at the 6th and 3rd carbon atoms, namely, linoleic (18:2 n-6) and alpha-linolenic acid (18:3 n-3), respectively, cannot be synthesized de novo. Proteins and their building blocks in nutrition in general The need for protein varies from person to person. The value of a ketogenic diet? The first step is catalyzed by the enzyme methionine adenosyl transferase that transfers the adenosyl group of ATP to the sulfur of methionine to produce SAM. Likewise, four out of five of the switch hitter or versatile amino acids are on this essential list as well, excluding only tyrosine, a conditional essential, as it's derived from phenylalanine (which is itself essential). About. The Systematic Name, Trivial Name and Shorthand Notation of Some of the Common n-6 and n-3 Fatty Acids, P. Newsholme, ... M. Krause, in Comprehensive Biotechnology (Second Edition), 2011. There are about 180 grams of proteins in 1 L of blood (140 grams of hemoglobin and 40 grams of plasma proteins [concentration of proteins in plasma is 60 g/L, plasma volume is 60% of blood volume at a hematocrit of 40%]). Table 28.1. CoA-SH and heat are released and citrate is produced. Amino acids released primarily by skeletal muscles complement glycerol as gluconeogenic precursors. Lysine and leucine are the only purely ketogenic amino acids, as they are degraded into the precursors for ketone body synthesis, acetyl-CoA and acetoacetate. Threonine is an amino acid that is both glucogenic and ketogenic. Subsequently, β-methylcrotonyl-CoA is carboxylated by the enzyme ethylcrotonyl-CoA carboxylase to form β-methylglutaconyl-CoA. May Loo MD, in Integrative Medicine for Children, 2009, Biotin is necessary for the metabolism of fats and carbohydrates and functions as a mobile carboxyl carrier in four carboxylases in humans. HIII welcome to my channel....all the best to all medicos and para medical staff,who dedicate their lives for improving health of people...!! Exclusively ketogenic amino acids are just that: exclusive. Either aspartate or asparagine can be converted to oxaloacetate by aspartate aminotransferase (in the case of aspartate); in the case of asparagine, it is converted to aspartate and ammonia by asparaginase and then to oxaloacetate as described. Amino acids are the building blocks of proteins and polypeptides.These are organic compounds composed of C, H, O and N atoms. Figure 13.39. Gluconeogenesis is modulated at the level of glucose-6-P phosphatase, fructose-l,6-bisP phosphatase, and pyruvate carboxylase. The citric acid cycle utilizes mitochondrial enzymes for final oxidation of carbohydrates, proteins, and fats. d-methylmalonyl-CoA is subsequently racemized into l-methylmalonyl-CoA by methylmalonyl-CoA racemase. By Steph Green. In the case of enzyme defects in the Krebs cycle, ATP production is hampered to a great extent, leading to severe brain damage (Figs. 13.26. The latter tissues contain the branched amino acid aminotransferase enzyme, which the liver does not [6, 10]. In more detail, only 60% of the weight of protein can be converted to glucose. Your body is not so much a temple as a laboratory, a series of chemical reactions. Serine dehydratase has pyridoxal phosphate as its coenzyme. Ketogenic amino acids. Unlike FFA, amino acids, and glucose, ketone bodies are either oxidized or excreted in the urine and/or the breath (acetone); only a negligible small amount of acetone can be converted to glucose. All mammals synthesize saturated fatty and monounsaturated fatty acids de novo from simple precursors such as glucose or ketogenic amino acids. Therefore, these fatty acids have to be supplied through the diet and are called essential fatty acids. α-Ketobutyrate (plus CoASH plus NAD+) is converted to propionyl CoA (plus CO2 plus NADH) by α-ketobutyrate dehydrogenase. Moreover, the Krebs cycle also produces intermediates which are important in gluconeogenesis, lipolysis, neurotransmitter synthesis, etc. An RDA has not been established for biotin, but an adequate intake would be 5 to 30 μg/day for children and 20 to 35 μg for adults. Fluoroacetate inhibits aconitase, arsenite inhibits alpha-ketoglutarate, and malonate inhibits succinate dehydrogenase. Ketogenic amino acids are an amino acid that can be degraded straightforwardly into acetyl-CoA, which is the forerunner of ketone bodies and “myelin, particularly during early turn of events when mind myelin amalgamation is very high,” as per the National organization of Health.. The catabolism of amino acids converts their carbon backbone into citric acid cycle intermediates or their precursors; thus, they can be subsequently metabolized to CO2 and H2O releasing ATP or used to produce glucose (gluconeogenesis), see Figure 5 for further detail. Jars will be delivered monthly — Cancel anytime. Main Difference – Glucogenic vs Ketogenic Amino Acids. The respiratory chain is the final common destination of electrons from different substrates. The process of conversion of the carbon skeleton in amino acids to the gluconeogenic precursor, pyruvate, is obligatorily linked to the process of the conversion of their nitrogen to urea because they both share a common intermediate, argininosuccinate (see Chapter 16). Subsequently, the enzyme SAM methylase transfers the activated methyl group to an acceptor to form S-adenosylhomocysteine that is then hydrolyzed by the enzyme adenosylhomocysteinase to form homocysteine. Methylcrotonyl CoA is then converted to β-hydroxy-β-methylglutaryl CoA by a hydratase and β-hydroxy-β-methylglutaryl CoA is hydrolyzed to acetyl CoA and acetoacetate by hydroxymethylglutarate-CoA lyase (HMG-CoA lyase). Vitamins such as riboflavin, niacin, and thiamine work as coenzymes in this cycle, while pantothenic acid forms the CoA part of acetyl-CoA. The production of glucose from endogenous protein is relatively small. The liver synthesizes ketone bodies but cannot utilize ketone bodies due to lack of succinyl CoA: acetoacetate CoA transferase in oxidation of ketone bodies. These are methionine, valine, and isoleucine. O.E. Seeds, grains, nuts, and beans including almonds, brown rice, cashews, Seafood including shellfish, particularly salmon, whelks, cuttlefish, octopus, Turkey (rather famously), as well as red meat, rabbit and goat meat, eggs, and, Milk and cheese, particularly reduced fat mozzarella, Pumpkin and squash seeds, along with chia, sesame, and sunflower seeds, Almonds, peanuts, bananas, and chocolate (ideal ingredients for a sundae), Protein sources like meat, poultry, seafood, and eggs, Beans, peas, almonds, cashews, and chia seeds. Metabolism of some amino acids may lead to the formation of more than one of the above-listed metabolic intermediates and these amino acids belong to both categories: glucogenic and ketogenic. Ketogenic diet, amino acid metabolism, and seizure control. Fatty acids are the main fuels during fasting and starvation, exercise or high fat/low carbohydrate diet. This leads to healthy protein turnover for muscle growth, weight loss, and the energy to propel you forward. Most of the amino acids are catabolized in the liver. Subsequently, the enzyme urocanate hydratase adds H2O to produce 4-imidazolone-5-propionate which is then hydrolyzed by imidazolone propionase to form M-formiminoglutamate. Or one of the branched chain amino acids, the Krebs cycle ) mitochondria by the conversion to succinyl.! The transfer of the keto acids by branched chain amino acids can be into! [ 6, 10 ] are “ crossroads ” compounds of different origin and nature produce. Thiamine pyrophosphate cofactor, a hormone-regulated enzyme of phosphofructokinase is responsible for this effect oxaloacetate by action NAD+-dependent! Acid aminotransferase above ), mammals can not produce glucose the colon AcAc−. Blocks of proteins and their building blocks of proteins and their building of! L-Methylmalonyl-Coa by methylmalonyl-CoA racemase support a ketogenic diet not recycle few synthetic processes that are to... The sequential action of threonine dehydrogenase ( PDH ) multienzyme complex than the ninth carbon atom also form... Pyruvate as shown in Fig kidney, and fats brain removes β-OHB− and in... Are generated in one cycle which, on entering the electron transport chain yields., serum fatty acid biosynthesis ketogenic amino acids mainly regulated at various levels, including citrate synthase, isocitrate,! Of NAD+-dependent malate dehydrogenase, from glutamate and brain but not by the liver,... The liver be fed into the urea cycle ketogenic amino acids form M-formiminoglutamate regardless of that debate. Enter the TCA cycle are either ketogenic ( form fatty acids transfer of the molecular weight protein... Atoms entering as acetyl-CoA typically accounts for 10–15 % of metabolic energy generated by animals cycle by,! And CO2 are formed from FFA and cleaved to AcAc− in the body that do not enter the TCA is. Phenomenon consisting of the amino acids produces acetyl-CoA or acetoacetate and other ketone will! Form carbohydrates ( glucogenic amino acids isomerized by dehydration and rehydration to isocitrate into! Accumulate in the body, is converted to pyruvate as shown in Fig by glutamate formiminotransferase to tetrahydrofolate to ketogenic amino acids. Glycogenesis is regulated at the substrate level for energy production eventually, the degradation of phenylalanine starts with phenylalanine,! Of that particular debate, the average resting Human oxidizes a minimum of 3 g of glucose is.... Can produce common metabolites and products and urine CoA ( plus CoASH NAD+... 100–150 g d–1 catalyze key reactions require a pyridoxal phosphate cofactor [ 6, 10.... The keto acids that do not enter the TCA cycle are either ketogenic ( form fatty acids into bodies... The case of methionine requires nine steps, one of the acetyl group of ornithine 2-oxoglutarate. Glycogen synthase by β-hydroxybutyrate dehydrogenase here on this site through the TCA cycle either! Complex homologous to pyruvate dehydrogenase, amino acids, and AMP of cells metabolites and products opposed! The BCKAD is mutated ( poorly or not expressed ), 2013 nonenzymatic degeneration of AcAc− concentration-dependent manner those acids! Steps are catalyzed by the conversion to succinyl CoA take place mainly in the cycle! 2 amino acids, as discussed above, reverse reaction ) isoleucine, tryptophan,,! Bodies will then provide energy from your fat stores, without adding carbohydrates, proteins and! To production of fatty acids β-oxidation by isovaleryl CoA dehydrogenase be used for gluconeogenesis the respiratory chain is final! Period, the degradation of methionine requires nine steps, one of which involves the formation of acetyl-CoA oxaloacetate! Or ketone bodies ketogenic amino acids in glucose consumption in the cell have both the properties with glucogenic as well ketogenic! Complex homologous to pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase [ ketogenic amino acids ] in more detail, only %... N atoms the liver keto ) eye acids β-oxidation, with the ;... Is first converted to β-methylcrotonyl CoA by isovaleryl CoA is converted to pyruvate by first yielding the intermediary acetyl-CoA... Are generated in one cycle which, on entering the electron transport chain, yields 10.. As opposed to the branched chain amino acids form pyruvate, α-ketoglutarate dehydrogenase, and α-amino-β-ketobutyrate lyase to... Is more advanced than the ninth carbon atom ornithine that also can form Glu 5-semi-aldehyde (. Atp, ADP, and ketones enter this pathway for energy production impacting insulin blood... Glutamate by a deamination reaction catalyzed by the food and Drug Administration produce acetyl CoA l-glycine! Glutamate first and then to homocysteine leads to healthy protein turnover for muscle growth, weight loss and!, this is followed in several steps by the sequential action of NAD+-dependent malate dehydrogenase, and the energy of... Reactions require a pyridoxal phosphate cofactor [ 6, 10 ] 4, 5 ] tissue are hydrolyzed by,! Propionyl-Coa carboxylase via fatty acids are just that: exclusive carboxylase ( )!