The pathways of formation of ammonia

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)

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