SEVEN AMINO ACIDS DEGRADED TO ACETYL COA

THE EXCRETION OF AMMONIUM IONS A part of NH4+ that is formed in the degradation of amino acids is used for the biosynthesis of nitrogen compounds. In most of the land living vertebrates the excess NH4+ is converted in urea and in that form is excreted. In birds and reptiles it is converted into uric acid and in aquatic animals it is directly excreted as urea.

DESTINATION OF DEGRADED AMINO ACID IN THE METABOLISM The carbon atoms of degraded amino acids are found in important intermediate products of the metabolism that can be converted into glucose or can be oxidized in the CITRIC ACID CYCLE. The carbon skeletons of the twenty amino acids are brought back to only seven molecules : pyruvate, acetyl CoA, acetoacetyl CoA, alpha-ketoglutarate, succinyl CoA, fumerate and oxaloacetate. Amino acids that are degraded to acetyl CoA are called KETOGENIC AMINO ACIDS because they can be converted into ketone bodies. The amino acids that are converted in the remaining of the seven molecules are called GLUCOGENIC AMINO ACIDS becaause they can be converted into phosphoenol pyruvate and then in glucose. Some amino acids are both ketogenic as well as glucogenic for example tyrosine, phenylalanine etc.

Some amino acids are both ketogenic as well as glucogenic for example tyrosine, phenylalanine etc.

The C3 family: alanine, serine and cystein is converted in pyruvate The C3 family: alanine, serine and cystein is converted in pyruvate. Pyruvate is the entry point for alanine, serine, cysteine, glycine, threonine and can be converted into pyruvate through different paths, by which the sulphur atom returns in hydrogen sulphide and sulphate. Also carbon atoms of amino acids glycine, threonine and tryptophan can be converted into pyruvate. The C4 family aspartate and asparagine are converted in oxaloacetate. Aspartate can also be converted in fumeratye by urea cycle. Fumerate is an entry point for half of the carbon atams of tyrosine ans phenylalanine. The C5 family glutamine, proline, arginine and hystidine are converted to alpha-ketaglutarate via glutamate. Alpha-ketoglutarate is the entry point for glutsamine, proline, arginine and hystidine that are first converted to glutam,ate. Succinate CoA is an entry point for single apolar amino acids by the transformation of threonine, isoleucine and valine via propionyl CoA. The pathway of propionyl CoA to succinate CoA is also present in thre oxidation of fatty acids with an odd number carbon atoms which are thus partial glucogenic, three of their carbon atoms can go in glucose.

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