Biomolecules Derived from Amino Acids

Tyrosine and Catecholamines

• Initial Conversion:
  • Tyrosine hydroxylase converts tyrosine to dopa
  • Requires tetrahydrobiopterin (BH4) as cofactor
  • Coupled to oxygen reduction to water
• Dopa to Dopamine:
  • Enzyme: aromatic amino acid decarboxylase
  • Removes carboxyl group, producing dopamine
  • Cofactor: paradoxical phosphate (PLP)
• Dopamine Functions:
  • Major role in brain's reward system and motor control
  • Parkinson's disease linked to underproduction
• Dopamine to Norepinephrine:
  • Enzyme: dopamine beta hydroxylase
  • Coupled to ascorbate reduction
• Norepinephrine to Epinephrine:
  • Enzyme: phenol ethanolamine and methyltransferase
  • Requires S-adenosyl methionine (SAM) as methyl donor
• Functions:
  • Norepinephrine: Alertness, arousal, fight or flight response
  • Epinephrine: Physiological effects like increased blood flow, pupil dilation

Tryptophan and Serotonin

• Initial Conversion:
  • Tryptophan hydroxylase converts tryptophan to 5-hydroxytryptophan
  • Coupled to tetrahydrobiopterin oxidation
• Serotonin Synthesis:
  • 5-hydroxytryptophan undergoes decarboxylation
  • Cofactor: PLP
• Serotonin to Melatonin:
  • Enzyme: serotonin N-acetyl transferase (SNAT)
  • Converted to melatonin in pineal gland
• Other Roles:
  • Tryptophan: Precursor to plant hormone and indole-3-acetate

Histidine and Glutamate

• Histidine to Histamine:
  • Enzyme: histamine decarboxylase
  • Cofactor: PLP
  • Role: Inflammatory reaction, neurotransmitter
• Glutamate to GABA:
  • Enzyme: PLP-dependent glutamate decarboxylase
  • Role: Major inhibitory neurotransmitter

Nitric Oxide from Arginine

• Enzyme: nitric oxide synthase
• Coupled to oxygen reduction and NADPH oxidation
• Functions: Vasodilation via soluble guanylate cyclase

Acetylcholine from Serine

• Conversion Steps:
  • Serine to ethanolamine
  • Ethanolamine to choline
  • Choline to acetylcholine
• Functions:
  • Chief neurotransmitter in neuromuscular junction
  • Role in parasympathetic nervous system

Coenzyme Derivatives from Amino Acids

• Niacin (Vitamin B3):
  • Derived from tryptophan
  • Precursor to NAD and NADP
• Coenzyme A:
  • Derived from cysteine
  • Role in fatty acid and pyruvate oxidation
• Folate (Vitamin B9):
  • Derived from glutamate
  • Role in one-carbon transfer reactions

Membrane Lipids from Serine

• Sphingolipids:
  • Glycine + palmitoyl-CoA
  • Forms sphingolipids like gangliosides
• Phospholipids:
  • Serine + CTP diacylglycerol forms phosphatidylserine (PS)
  • PS can be converted to phosphatidylethanolamine (PE) and phosphatidylcholine (PC)

Polyamines from Ornithine

• Initial Conversion:
  • Enzyme: ornithine decarboxylase
  • Produces putrescine
• Polyamine Synthesis:
  • Putrescine + decarboxylated SAM form spermidine and spermine
  • Role: DNA packaging

Carnitine and Creatine

• Carnitine:
  • Derived from trimethyllysine
  • Role: Transporting fatty acids into mitochondrial matrix
• Creatine:
  • Derived from glycine and arginine
  • ATP buffer in muscle tissues

Glutathione

• Derived from glutamate, cysteine, and glycine
• Role: Antioxidant against hydrogen peroxide

Heme from Glycine

• Heme Synthesis:
  • Glycine + succinyl-CoA
  • Series of reactions produce protoporphyrin
  • Protoporphyrin + iron forms heme
• Heme Breakdown:
  • Heme to biliverdin (releases CO and iron)
  • Biliverdin to bilirubin
  • Bilirubin transported as bilirubin-glucuronide
  • Role: Oxygen transport in blood

Bile and Bilirubin

• Bile Synthesis:
  • Cholesterol in liver forms bile salts
  • Primary bile acids conjugated with taurine or glycine
• Bilirubin Metabolism:
  • Bilirubin transformed in liver and emulsified with bile salts
  • Microbial enzymes convert bilirubin to urobilinogen in intestines
  • Urobilinogen in kidneys converts to urobilin (yellow color of urine)
  • Remaining urobilinogen forms stercobilin (brown color of feces)