Ketogenic and Glucogenic Amino Acids

Ketogenic and glucogenic amino acids can convert to Main Powerhouse molecules. Nonessential amino acids can be produced directly or indirectly from Main Powerhouse molecules. 

Following their deamination, several amino acids can be converted into oxaloacetate via pyruvate or other components of the TCA cycle these are termed glucogenic amino acids because their carbon atoms may eventually appear in glucose (see Table 6.7). The carbon skeletons of other amino acids may be converted into acetyl-CoA or acetoacetyl-CoA and these are ketogenic amino acids. A few amino acids be metabolized through both glucogenic and ketogenic pathways. 

Glucogenic amino acids Ketogenic amino acids Amino acids that are glucogenic and ketogenic... 

Figure 9-3. Fates of the carbon skeletons upon metabolism of the amino acids. Points of entry at various steps of the tricarboxylic acid (TCA) cycle, glycolysis and gluconeogenesis are shown for the carbons skeletons of the amino acids. Note the multiple fates of the glucogenic amino acids glycine (Gly), serine (Ser), and threonine (Thr) as well as the combined glucogenic and ketogenic amino acids phenylalanine (Phe), tryptophan (Trp), and tyrosine (Tyr). Ala, alanine Cys, cysteine lie, isoleucine Leu, leucine Lys, lysine Asn, asparagine Asp, aspartate Arg, arginine His, histidine Glu, glutamate Gin, glutamine Pro, proline Val, valine Met, methionine.

Amino acids whose catabolism yields either acetoacetate or one of its precursors, acetyl CoA or acetoacetyl CoA, are termed ketogenic. Tyrosine, phenylalanine, tryptophan, and isoleucine are both ketogenic and glucogenic. Leucine and lysine are solely ketogenic. 

According to a long-used classification amino acids are ketogenic if (like leucine) they are converted to acetyl-CoA (or acetyl-CoA and acetoacetate). When fed to a starved animal, ketogenic amino acids cause an increased concentration of acetoacetate and other ketone bodies in the blood and urine. On the other hand, glucogenic amino acids such as valine, when... 

Figure 23.21. Fates of the Carbon Skeletons of Amino Acids. Glucogenic amino acids are shaded red, and ketogenic amino acids are shaded yellow. Most amino acids are both glucogenic and ketogenic.

Figure 26-8 Metabolic relations among intermediates of carbohydrate, fat, and protein metabolism. Note that acetyi-CoA is produced from both carbohydrate and fat,The glucogenic amino acids, derived from protein metabolism, enter glycolytic paths as a-lceto acids. Ketogenic amino adds enter as acetyl-CoA.

Some amino acids are classified as both ketogenic and glucogenic. Review the Q U ESTI N 1 5.4... 

Amino acids are classified as ketogenic or glucogenic on the basis of whether their carbon skeletons are converted to fatty acids or to glucose. Several amino acids can be classified as both ketogenic and glucogenic because their carbon skeletons are precursors for both fat and carbohydrates. 

The following amino acids are both ketogenic and glucogenic phenylalanine, isoleucine, lysine, tryptophan, and tyrosine. 

Metabolism of amino acids to form common metabolic intermediates. This figure depicts the major fate of the amino acids that form common metabolic intermediates. Those formed above the dotted line are ketogenic and those formed below are glucogenic. Any amino acid followed by (p) is found both above and below the dotted line. As the (p) indicates, this amino acid produces both ketogenic and glucogenic products during metabolism. 

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