Definition of leucine in US English:



  • A hydrophobic amino acid which is a constituent of most proteins. It is an essential nutrient in the diet of vertebrates.

    Chemical formula: (CH₃)₂CHCH₂CH(NH₂)COOH

    • ‘In simple terms, BCAAs are made up of three amino acids: leucine, isoleucine and valine.’
    • ‘The amino acids arginine and leucine are noncarbohydrate inducers of insulin.’
    • ‘The aspartate can be used as a precursor for the synthesis of other amino acids such as asparagine, threonine, isoleucine, leucine, valine, lysine, and methionine.’
    • ‘Key essential amino acids are valine, leucine, isoleucine, tryptophan and methionine.’
    • ‘Taking supplemental leucine with other essential amino acids from whey protein may accelerate muscular gains.’


Early 19th century: coined in French from Greek leukos ‘white’ + -ine.