The word enkephalin is taken to mean any peptide that has the sequence Tyr-Gly-Gly-Phe-Xaa. Hence [Leu5]enkephalin which may often be written as [Leu]enkephalin, designates one of the natural peptides. It is important to use square brackets, the symbols for substitution, and not a hyphen, which would indicate N-terminal extension, i.e. Leu-enkephalin would be Leu-Tyr-Gly-Gly-Phe-Xaa.
1. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), and Nomenclature Commission of IUB (NC-IUB),.Newsletter 1984, Arch. Biochem. Biophys., 1984, 229, 237-245; Biochem. Internat., 1984, 8, following p 202; Biochem. J., 1984, 217, I-IV; Biosci. Rep., 1984, 4, 177-180; Chem. Internat., 1984(3), 24-25; Eur. J. Biochem., 1984, 138, 5-7; Hoppe-Seyler's Z. Physiol. Chem., 1984, 365, I-IV; Trends Biochem. Sci., 1984, 9, various issues.