Gamma-aminovoihappo muodostuu glutamaatista, kun sen toinen -COOH pääty dekarboksyloituu. jolloin jää jäljelle 4C- voihappo-runko, jonka päätyhiilessä on NH2-ryhmä.
(H2N)C-CH2-CH2-COOH , gamma- amino voihappo,
Hiiliasemien nimet: C gamma - C beta- C alfa - C-pääty
Harper 1969 sivulta 350-2.
- In the centrl nervous system amino acid glutamate (GLU) plays a special role in brain metabolism. For example, the transport of potassium (kalium) to the brain is accomplished by glutamate. The role of glutamate (GLU) in detoxifying ammonia (NH3) in the brain by formation of glutamine (GLN) should also be recalled.
- Decarboxylation of glutamate (GLU) produces gamma-aminobutyrate (GABA). An enzyme which catalyzes its formation from glutamte (GLU) by alpha-decarboxylation is found in tissues of the central nervous system, principally in the gray matter of the brain. This enzyme requires pyridoxal phosphate ( B6 vitamine) as a coenzym.
(Comment: Glutamate COOH- CH(NH2)-CH2-CH2-COOH has 5 carbon, The both ends have a carboxylgroup -COOH.
One of them decarboxylates. That means: CO2- group leave the molecule from the alfa- carbon)
GABA has 4 carbons left:
Compare (C4:0) usual Butyrate , short chain fatty acid, It has four carbons C-C-C-COOH
but GABA has still NH2- aminogroup in the butyrate chain. Its place is called gamma, the third carbon from the caerboxylated end of this amino-butyrate-species:
(H2N)C-CH2-CH2-COOH , gamma- amino butyric acid)
- Gamma-aminobutyric acid is now known to serve as a normal regulator of neuronal activity, being active as an inhibitor when studied in various reflex preparations. (1969!).
- it is further metabolized by deamination to succinic semialdehyde. The deamination is accomplished by a pyridoxal-dependent enzyme and the ammonia removed is transaminated to ketoglutarate (alfa-KG) , thus forming more glutamate (GLU)
(And how the GABA itself after forming succinic semialdehyd without nitrogen?)
- Succinic semialdehyde may then be oxidized to succinate ( and so to take part in citron acid cycle, oxidative metabolism)
- or it can be reduced to gamma-hydroxybutyrate GHB, which has been found to exist in the brain in significant amounts.
- According to Fishbein et Bessman (1964), reduction of succinic semialdehyde by homogenates of brain can be accomplished by an enzyme in the soluble protein fraction which was indistingguishable from lactic dehydrogenase.
- When succinic semialdehyde is oxidized to succinic acid, there is completed what amounts to a bypass around the citric acid sycle in the brain in the sense that ketoglutarate (KG) , rather than going directly to succinate ( as in the citric acid cycle), is transaminated to glutamate (GLU) and thence by decarboxylation to gamma-aminobutyrate (GABA), which is the source of succinic semialdehyde to form succinate.
- Gamma-aminobutyrate has also been detected in the kidneys of humans, indicating that this compound is not unique of the central nervous system in man (1966). (Comment: E.g. pancreatic beta-cells use GABA-GLU cycle, when producing glucose homeostasis to the bloodcircualtion).