Leucine (symbol
Leu or
L) is an essential amino acid
that is used in the biosynthesis
of proteins
. Leucine is an α-amino acid, meaning it contains an α-amino group
(which is in the protonated −NH
3+ form under biological conditions), an α-carboxylic acid group
(which is in the deprotonated −COO
− form under biological conditions), and a side chain isobutyl group
, making it a non-polar aliphatic amino acid. It is essential in humans, meaning the body cannot synthesize it: it must be obtained from the diet. Human dietary sources are foods that contain protein, such as meats, dairy products, soy products, and beans and other legumes