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Amino acid degradation oxaloacetate

The acetyl-CoA derived from amino acid degradation is normally insufficient for fatty acid biosynthesis, and the acetyl-CoA produced by pyruvate dehydrogenase and by fatty acid oxidation cannot cross the mitochondrial membrane to participate directly in fatty acid synthesis. Instead, acetyl-CoA is linked with oxaloacetate to form citrate, which is transported from the mitochondrial matrix to the cytosol (Figure 25.1). Here it can be converted back into acetyl-CoA and oxaloacetate by ATP-citrate lyase. In this manner, mitochondrial acetyl-CoA becomes the substrate for cytosolic fatty acid synthesis. (Oxaloacetate returns to the mitochondria in the form of either pyruvate or malate, which is then reconverted to acetyl-CoA and oxaloacetate, respectively.)... [Pg.804]

We now turn to the fates of the carbon skeletons of amino acids after the removal of the a-amino group. The strategy of amino acid degradation is to transform the carbon skeletons into major metabolic intermediates that can be converted into glucose or oxidized by the citric acid cycle. The conversion pathways range from extremely simple to quite complex. The carbon skeletons of the diverse set of 20 fundamental amino acids are furmeled into only seven molecules pyruvate, acetyl CoA, acetoacetyl CoA, a-ketoglutarate, succinyl CoA, fumarate, and oxaloacetate. We see here a striking example of the remarkable economy of metabolic conversions, as well as an illustration of the importance of certain metabolites. [Pg.966]

AMINO ACIDS FORMING OXALOACETATE Both aspartate and asparagine are degraded to form oxaloacetate. Aspartate is converted to oxaloacetate with a single transamination reaction. Asparagine is initially hydrolyzed to yield aspartate and NHJ by asparaginase. [Pg.519]

The metabolic products of amino acid degradation are acetyl-CoA, acetoacetyl-CoA, pyruvate, a-ketoglutarate, succinyl-CoA, fumarate, and oxaloacetate. [Pg.727]

The alanine cycle accomplishes the same thing as the Cori cycle, except with an add-on feature (Fig. 17-11). Under conditions under which muscle is degrading protein (fasting, starvation, exhaustion), muscle must get rid of excess carbon waste (lactate and pyruvate) but also nitrogen waste from the metabolism of amino acids. Muscle (and other tissues) removes amino groups from amino acids by transamination with a 2-keto acid such as pyruvate (oxaloacetate is the other common 2-keto acid). [Pg.235]

The degradation of most amino acids is anaplerotic, because it produces either intermediates of the cycle or pyruvate glucogenic amino acids see p. 180). Gluconeogenesis is in fact largely sustained by the degradation of amino acids. A particularly important anaplerotic step in animal metabolism leads from pyruvate to oxaloacetic acid. This ATP-dependent reaction is catalyzed by pyruvate... [Pg.138]

Eugene Kennedy and Albert Lehninger showed in 1948 that, in eulcaiyotes, the entire set of reactions of the citric acid cycle takes place in mitochondria. Isolated mitochondria were found to contain not only all the enzymes and coenzymes required for the citric acid cycle, but also all the enzymes and proteins necessaiy for the last stage of respiration—electron transfer and ATP synthesis by oxidative phosphoiylation. As we shall see in later chapters, mitochondria also contain the enzymes for the oxidation of fatty acids and some amino acids to acetyl-CoA, and the oxidative degradation of other amino acids to a-ketoglutarate, succinyl-CoA, or oxaloacetate. Thus, in nonphotosynthetic eulcaiyotes, the mitochondrion is the site of most energy-yielding... [Pg.606]

The TCA cycle, strictly speaking, has only one input fuel— acetyl-CoA. Catabolism of carbohydrates and fats leads to the production of acetyl-CoA, so that the TCA cycle is ideally suited to serve as the major oxidative sequence in the catabolism of those types of compounds. However, degradation of the amino acids that result from the hydrolysis of protein produces a number of intermediates, among which are a-ketoglutarate, succinyl-CoA, and oxaloacetate (chapter 22). a-Ketoglutarate and succinyl-CoA, can be oxidized... [Pg.295]

Degradation of amino acids produces a number of intermediates, among which are a-ketoglutarate, suc-cinyl-CoA, and oxaloacetate. a-Ketoglutarate and suc-cinyl-CoA can be oxidized to oxaloacetate, but the cycle as such cannot oxidize oxaloacetate further. Oxaloacetate is oxidized further by first converting it to phosphoenolpyruvate. This permits the total oxidation of oxaloacetate to C02 by the enzymes of the TCA cycle. [Pg.302]

Oxoglutarate Succinyl-CoA Oxaloacetate Fumarate 2-Oxoglutarate Oxaloacetate Glutamate Degradation of some amino acids (Chap. 15) Aspartate... [Pg.355]

A smaller number of amino acids are degraded to acetyl-CoA or acetoacetyl-CoA. Neither acetyl-CoA nor acetoacetyl-CoA can yield a net production of oxaloacetate, the precursor for the gluconeogenesis pathway (because for every 2-carbon acetyl residue entering the TCA cycle, two carbon atoms leave as CO2). These are referred to as the ketogenic amino acids they can be catabolised for energy in the TCA cycle, or converted to ketone bodies or fatty acids, but they caimot be converted to glucose. [Pg.42]

The acetyl CoA that gets on the ferris wheel can be continually replenished through glucose breakdown, or, mainly, through fatty acid degradation (oxidation), or by transformation of certain amino acids. What, however, produces the seats of the ferris wheel, or replenishes them when necessary The seats cannot be replaced by acetyl CoA, which is merely a passenger. The chemicals of the ferris wheel can be restored in part by certain amino acids that can convert to Krebs cycle intermediates. There also is an important side step in which pyruvate can be directly convert to oxaloacetate (D-8). [Pg.10]

Thus far, discussion has focused on the citric acid cycle as the major degradative pathway for the generation of ATP. As a major metabolic hub of the cell, the citric acid cycle also provides intermediates for biosyntheses (Figure 17,19). For example, most of the carbon atoms in porphyrins come from succinyl CoA. Many of the amino acids are derived from a -ketoglutarate and oxaloacetate. These biosynthetic processes will be discussed in subsequent chapters. [Pg.720]

Figure 7-7. Degradation of amino acids. (A) Amino acids that produce pyruvate or intermediates of the TCA cycle. (B) Amino acids that produce acetyl CoA or ketone bodies. OAA = oxaloacetate HMG CoA = hydroxy-methylglutaryl CoA. Figure 7-7. Degradation of amino acids. (A) Amino acids that produce pyruvate or intermediates of the TCA cycle. (B) Amino acids that produce acetyl CoA or ketone bodies. OAA = oxaloacetate HMG CoA = hydroxy-methylglutaryl CoA.
Tie reactions constitute a metabolic motif that we will see again in fatty acid synthesis and degradation as well as in the degradation of some amino acids. A methylene group (CH2) is converted into a carbonyl group (C=0) in three steps an oxidation, a hydration, and a second oxidation reaction, Oxaloacetate is thereby regenerated for another round of the cycle, and more energy is extracted in the form of FADH and NADH. [Pg.487]

Although diverse in structure, most amino acids lead to a few central compounds that flow into the major metabolic pathways. All of them effectively produce pyruvate, a-ketoglutarate, oxaloacetate, succinate, fumarate, acetoacetate, or acetyl CoA (Fig. 19.6). Therefore, a large number of unusual compounds are not formed, which would require a new set of enzymatic machinery for metabolism. This is also advantageous because the carbons from degraded amino acids can be funneled into the major pathways of metabolism with normal metabolic controls. [Pg.532]


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See also in sourсe #XX -- [ Pg.668 ]




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Acid degradation

Amino acids degradation

Amino degradation

Oxaloacetate

Oxaloacetic acid

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