Figure 2.

Elimination of amino-acids.

The carbon skeletons of amino acids are broken down into metabolites that can either be oxidized into CO₂ and H₂O to generate ATP, or can be used for gluconeogenesis. The catabolism of amino acidsaccounts for 10 to 15% of the human body’s energy production. Each of the 20 amino acids has aseparate catabolic pathway, yet all 20 pathways converge into 5 intermediates, all of which can enter thecitric acid cycle. From the citric acid cycle the carbon skeletons can be completely oxidized into CO₂ or diverted into gluconeogensis or ketogenesis. Glucogenic amino acids are broken down into one of the following metabolites: pyruvate, α-ketoglutarate, succinyl CoA, fumarate or oxaloacetate. Ketogenic amino acids are broken down intoacetoacetate or acetyl-CoA. Larger amino acids, tryptophan, phenylalanine, tyrosine, isoleucine andthreonine are both glucogenic and ketogenic. Only two amino acids are purely ketogenic they are lysine and leucine. If two of the amino acids are purely ketogenic and five amino acids are both ketogenic and glucogenic, than that leaves 13 amino acids that are purely glucogenic: Arginine, Glutamate, Glutamine, Histidine, Proline, Valine, Methionine, Aspartate, Asparagninen, Alaanine, Serine, Cysteine, and Glycine [87].