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Ammonia is formed in all tissues, particularly in brain. There are next pathways of formation of ammonia:
deamination of amino acids
deamination of purine bases
deamination of pyrimidine bases
deamination of hexose amines
deamination of cadaverine and putrescine
the cleavage of amides
oxidative deamination of biogenic amines
Deamination is a main catabolic process which occurs with amino acids. There are following kinds of deamination of amino acids:
hydrolytic deamination
amino acid+H2Oàhydroxyacid+NH3
reductive deamination:
amino acid+NADH2àsaturated fatty acid+NH3+NAD
intramolecular deamination:
amino acid (aspartic acid) à unsaturated fatty acid (fumaric acid) + NH3
oxidative deamination of glutamic acid (indirect deamination). This kind of deamination is a main one. Only glutamic acid undergoes the oxidative deamination, because its dehydrogenase is active in physiologic conditions. Dehydrogenases of other amino acids are inactive in physiologic conditions therefore other amino acids firstly must be converted into glutamic acid through transamination with alfa-ketoglutaric acid. Hence, this kind of deamination is also named as indirect deamination and consists of 2 stages - transamination and oxidative deamination of glutamic acid:
alanine+alfa-ketoglutaric acid↔pyruvic acid+glutamic acid
aspartic acid+ alfa-ketoglutaric acid↔oxalo-acetic acid+glutamic acid
Thus, deamination of amina acids results in formation of nitrogenless residues of amino acids (predominantly ketoacids) and ammonia.
Nitrogenless residues can be used for gluconeogenesis, liponeogenesis, ketogenesis, transamination and citric acid cycle. Mainly nitrogenless residues of amino acids are used in citric acid cycle (CAC). The next nitrogenless residues of amino acids are formed and beside of CAC they are used in following processes:
pyruvic acid (repeat, please, reactions of glycolysis, transamination with pyruvic acid, gluconeogenesis);
alfa-ketoglutaric acid which is used for formation of Glu and Gln
succinylCoA is used on heme synthesis
oxaloacetate is used on gluconeogenesis, liponeogenesis, formation of Asn and transamination;
fumaric acid
acetoacetylCoA is used on ketogenesis
Oxidative deamination of biogenic amines
Biogenic amines are destroyed by MAO and DAO. Oxidative deamination of amines occurs in 2 stages:
histamine+FADàhistimine+FADH2
histimine+H2Oàcorresponding aldehyde+NH3
FPH2 is oxidized by itself under action of molecular oxygen. It results in formation of H2O2: FPH2 + O2 à FP + H2O2 (2H2O2à 2H2O + O2)
The digestion of carbohydrates | Gluconeogenesis and Cori cycle | The importance of Lipids | The absorption of products of Lipids digestion | The formation, composition, role and metabolism of lipoproteins (LP) | Beta-oxidation of FFA and its energetic value | The biosynthesis of FFA | Obesity and fat infiltration of a liver | Biochemistry of atherosclerosis | The digestion of Proteins |