The discovery of leucine

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Leucine is a naturally occurring essential amino acid with the chemical formula C6H13NO2. Leucine is obtained by the hydrolysis of pancreatic enzymes during digestion and is necessary for optimal growth in children and for the maintenance of nitrogen balance in adults[1].


The French chemist Joseph Louis Proust discovered[2] leucine in 1819 after fermenting gluten. The process he used is described in his 1819 publication in the following manner:

  • Gluten was first fermented. The same gluten was then washed and put into a jar for a few days.
  • The gluten was then placed in a silver bowl and slowly heated to the consistency of a syrup. He noted that the surface in contact with the gluten blackened due to hydrogen sulphide from the gluten reacting with the silver.
  • The thick syrup was left in the silver bowl for a few days to solidify. He noted it having an acrid cheese-like flavour.
  • He then filled the bowl with the solid gluten with alcohol and observed the formation of a cloudy solution due to an abundant amount of white substance separating from the gluten.
  • He then filtered the solution and washed the filtrate with alcohol until it no longer tasted like cheese.

Here is a photograph[3] of pure leucine:


Here is a portrait[4] of Joseph Louis Proust: