Leucine is a white, soluble, essential amino acid found in proteins. Its chemical formula is: (CH₃)₂ CHCH₂ CHNH₂ COOH and it is also known α-aminoisocaproic acid. Leucine is one of the most common of the amino acids obtained from proteins. It can be obtained by fractional crystallization of hydrolysed proteins. It is optically active. Melting point 293–295°C (decomp).