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Histidine is a naturally occuring essential amino acid with the chemical formula C6H9N3O2. It is necessary for tissue growth and repair[1].


The German biochemist Ludwig Karl Martin Leonhard Albrecht Kossel discovered[2] histidine in 1896 while studying sturine (a protamine in the spermatozoa of sturgeon). Here is how he isolated histidine from it:

  • He first mixed 20 g of sturine sulphate with 60 g of concentrated sulphuric acid and 120 cm3 of water and boiled the solution for 8 hours in a reflux condenser.
  • Barium hydroxide was then added to the solution until the sulphuric acid was removed.
  • The excess barium was removed by adding carbonic acid to the solution. The solution was then filtered and mercuric chloride added to it, upon which a precipitate formed.
  • He then added hydrogen sulphide to the precipitate to free it from mercury.
  • After several days, thick pale crystals of histidine began to form in the solution.

Here is a photograph[3] of histidine crystals:


Here is a photograph[4] of Albrecht Kossel: