Occurs in two stages
- Transfer of the amino group to the coenzyme pyridoxal phosphate (PLP) (bound to the coenzyme) to form pyridoxamine phosphate.
- The amino group of pyridoxamine phosphate is then transferred to a keto acid to produce a new amino acid and the enzyme with PLP is regenerated.
- All the transaminases require pyridoxal phosphate (PLP), a derivative of vitamin B6.
- Important for the redistribution of amino groups and production of non-essential amino acids. It involves both catabolism (degradation) and anabolism (synthesis) of amino acids.
- Transamination diverts the excess amino acids towards energy generation.
- The amino acids undergo transamination to finally concentrate nitrogen in glutamate. Glutamate is the only amino acid that undergoes oxidative deamination to a significant extent to liberate free NH3 for urea synthesis.
- All amino acids except lysine, threonine, proline and hydroxyproline participate in transamination.
- The effects produced due to elevation in blood NH3 levels
- Elevation in blood NH3 level may be genetic or acquired.
- Gentic is impairment in urea synthesis due to a defect in any one of the five enzymes .
- The acquired hyperammonemia may be due to hepatitis, alcoholism etc. where the urea synthesis becomes defective, hence NH3 accumulates.
- Accumulation of NH3 shifts the equilibrium to the right with more glutamate formation, hence more utilization of D-ketoglutarate.
- D- Ketoglutarate is a key intermediate in TCA cycle and its depleted levels impair the TCA cycle.
- The net result is that production of energy (ATP) by the brain is reduced. The toxic effects of NH3 on brain are, therefore, due to impairment in ATP formation.
- When the plasma level of ammonia is highly elevated, intravenous administration of sodium benzoate and phenyllactate is done.
- These compounds can respectively condense with glycine and glutamate to form water soluble products that can be easily excreted.