Histidine is a naturally occuring essential amino acid with the chemical formula C6H9N3O2. It is necessary for tissue growth and repair.
The German biochemist Ludwig Karl Martin Leonhard Albrecht Kossel discovered 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 of histidine crystals: