Amino Acid Biosynthesis

• amino acid biosynthesis uses glutamate dehydrogenase (just like for degradation!), but this time it goes from alpha-ketoglutarate to glutamate
• • the NH4+ comes from nitrogenase activity
  • the second step is stereospecific

  A) alpha-ketoglutarate

  B) glutamate

  C) NADPH

  D) NADP+

  
• For amino acid biosynthesis, all amino groups come from glutamate.
• For amino acid biosynthesis, the carbon skeletons come from intermediates of glycolysis or gluconeogenesis, TCA, and PPP.
• nonessential amino acids = can be synthesized by humans

  essential amino acids = cannot be synthesized by humans
• Shikimate pathway = forms the precursor molecule (chorismate) for aromatic amino acids

  • uses PEP from glycolysis or gluconeogenesis
  • uses E4P from PPP
• tryptophan synthase = attaches indole to serine to make tryptophan

  • alpha subunit: makes indole from indole-3-glycerol phosphate (formed from chorismate from the Shikimate pathway), releases GAP!
  • beta subunit: attaches the indole to serine using PLP
• in tryptophan synthase, the alpha and beta subunits are attached by a tunnel, which serves several purposes:

  • indole is not lost between the alpha and beta subunits
  • increases effective concentration of indole substrate for the beta subunit
  • synchronizes alpha and beta subunit activity