16. Synthesis of biologically active molecules from amino acids

Last updated on November 19, 2018 at 17:16

Summary

  • The precursor of heme is succinyl-CoA
  • Heme is degraded into biliverdin and CO
  • Creatine is synthesized from glycine and arginine
  • Glutathione is synthesized from glutamate, cysteine and glycine
  • All catecholamines (dopamine, norepinephrine, epinephrine) come from tyrosine
  • Serotonin comes from tryptophan
  • Histamine comes from histidine
  • GABA comes from glutamate
  • NO comes from arginine
  • Polyamines come from methionine and ornithine

If you know the above you should be good, but still

Heme, the functional group that binds to iron in haemoglobin, is synthesized from succinyl-CoA. 8 Succinyl-CoA are combined and go through many reactions, where they become a type of molecule called porphyrins, until they end up as heme. Porphyrias are genetic diseases where there are defects in one of the enzymes required.

Heme is degraded to biliverdin and CO. The latter is a vasodilator, but toxic in high concentrations. Biliverdin is reduced to bilirubin, which is an important antioxidant in the blood. Bilirubin then enters a pathway to end up as urobilin as stercobilin, which are excreted in urine and feces, respectively. Jaundice is the condition in which biliverdin in the blood increases, and the skin turns yellow.

Creatine is synthesized from glycine and arginine. It can be phosphorylated to phosphocreatine, which acts as a “storage” of ATP. During hard exercise, phosphocreatine can regenerate ATP by losing its phosphate group.

Glutathione is synthesized from glutamate, cysteine and glycine. Glutathione is an important antioxidant, which serves as a reducer, maintains iron in Fe2+ and detoxifies peroxides that are formed during the metabolism.

Catecholamines are synthesized from tyrosine. They are dopamine, norepinephrine and epinephrine. The synthesis of the latter two also requires vitamin C. Dopamine is an excitatory neurotransmitter. Neurotransmitters are molecules that transmit signals in the nervous system. Excitatory means that it “excites” the brain, unlike inhibitory neurotransmitters, which do the opposite. In Parkinson’s, dopamine is underproduced. The treatment is supplement of DOPA, the direct precursor of dopamine. Dopamine is not given because it cannot cross the blood-brain barrier, however DOPA can.

Histamine is a vasodilator, that is also released in allergic responses. It also stimulates acid secretion in the stomach. It is synthesized from histidine.

Serotonin is another neurotransmitter, but it is inhibitory, unlike dopamine. It is synthesized from tryptophan.

GABA is also an inhibitory neurotransmitter. It is synthesized from glutamate, and is underproduced in epilepsy.

Polyamines are synthesized from methionine and ornithine. They are involved in DNA packaging.

Nitric oxide (NO) is synthesized from arginine. It is a neurotransmitter and a vasodilator.


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15. Enzymopathies of amino acid metabolism

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17. Nucleotide synthesis and degradation

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