36 - Synthesis and biological role of specialized products from arginine (synthesis of creatine phosphate, citrulline, nitric oxide, polyamines), serine (synthesis of ethanolamine, choline, phospholipids, sphingolipids), tryptophan (synthesis of serotonin, melatonin, NAD+), tyrosine (synthesis of thyroid hormones, catecholamines, melanin). Central role of glutamate and glutamine in metabolism of nitrogen compounds. Role of glutathione.

sections

• creatine phosphate

• citrulline

• tryptophan

• serotonin

• melatonin

• Tyrosine

• synthesis of T3 + T4

• melanin

• glutathione

• Glutamate

• glutamine

• creatine phosphate

• localised = kidney, liver, muscle and brain

• role - energy reserve in muscle

• synthesis - arginine, glycine + methionine required

• citrulline

• synthesis - arginine and nitric oxide synthase recquired

• L- arginine precursor for polyamines (high cationine compounds that bind DNA + RNA)

• tryptophan

• essential amino acids

• precursor for serotonin + melatonin

• serotonin

• location - serotoninergic neurons and enterochromaffin cells

• role - regulate body temp, pain, mood, sleep

• activates platelet aggregation, smooth muscle contraction

• melatonin

• location - pineal gland

• obtained by methylation of serotonin synthesis + secretion increases at night

• Tyrosine

• helps synthesise catecholamines

• NA + A → synthesised in adrenal medulla + act in response to stress

• regulation - tyrosine hydroxylase

• synthesis of T3 + T4

1. iodine enters thyrocyte via Na/I symport

2. Thyroglobulin synthesis

3. exocytosis to thyroid follicle lumen

4. oxidation of iodine

5. iodination

6. conjugation

7. endocytosis into lysosome

8. proteolysis

9. T3 + T 4 secreted into blood stream

• melanin

• pigment

• produced by melanocytes

• stimulated by UV → a photo protectant - absorbs harmful UV and transforms into harmless heat

• deficiency → albinism

• glutathione

• most abundant water soluble thiol molecule

• donor of H in reduction reactions

• important cell antioxidant

• transport amino acids

glutamate

• provides nitrogen for AA synthesis

• Gives amino group to oxaloacetate so aspartate and ketoglutarate are formed

• involved in synthesis of GABA

• involved in synthesis of glutathione

glutamine

• main transport nontoxic form of ammonia in blood

• depot of non toxic ammonia that can be used in:

  • asparagine

  • synthesis of purine

  • synthesis pf amino sugars

  • source of ammonia in kidneys (for synthesis and secretion of NH4+)