Glutamic acid

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Glutamic acid is a nonessential amino acid with the chemical formula C5H9NO4. It is used principally in the biosynthesis of proteins and an important metabolic intermediate[1].


The German chemist Karl Heinrich Leopold Ritthausen discovered[2] glutamic acid in 1866 while experimenting on wheat gluten. In his publication[2], he explains the method by which he isolated glutamic acid:

  • 2 parts of wheat gluten was boiled with 5 parts of sulphuric acid and 13 parts of water for 20-24 hours. He used a Liebig condenser to replace the evaporated water and make it flow back into the solution.
  • A black-brown solution was then obtained with lumps of black substance floating on it. The solution was filtered and calcium hydroxide added to it. This resulted in the precipitation of gypsum (calcium sulphate dihydrate) which was then filtered out.
  • The filtrate was then boiled to about two-thirds its initial volume. This was filtered again to remove precipitated minerals (mainly calcium carbonate). Oxalic acid was then added to the filtrate to precipitate any remaining calcium, which was then filtered.
  • The excess oxalic acid in the filtrate was removed by boiling the solution with lead carbonate.
  • The excess lead in the solution was removed as a sulphide and the remaining solution was evaporated to a small volume.
  • The solution was left to stand for a few days which then resulted in the formation of crystals (mostly containing tyrosine). These crystals were filtered out and hot water was gently added to them in order to dissolve the substances that adhered to the crystals, and not the crystals themselves.
  • The solution which contained the dissolved substances was then cooled to a syrupy consistency and contained mostly crystals of leucine.
  • The crystals were filtered out and dissolved in boiling water. This solution was then left to crystallise, to which 30 percent warm alcohol was then added to completely dissolve the leucine.
  • This finally resulted in the precipitation of glutamic acid. The dissolved leucine was poured away and the precipitate added to 30 percent alcohol. The solution was boiled and then cooled to recrystallise the glutamic acid.

He then proceeded to determine the chemical formula of his discovery, which he did as C5H9NO4. Here is a photomicrograph[3] of glutamic acid crystals:


Here is a photograph[4] of Heinrich Ritthausen: