Abbreviations and Symbols for the Description of the Conformation of Polypeptide Chains

These rules are based on "A proposal of standard conventions and nomenclature for the description of polypeptide conformation" (Edsall et al., 1966) and have been prepared by a subcommission set up by the IUPAC-IUB Commission on Biochemical Nomenclature in 1966.lThe original proposals have been modified so as to bring them as far as possible into line with the system of nomenclature current in the fields of organic and polymer chemistry.Two recommendations are appended to the rules, the first dealing with the terms configuration and conformation and the second with primary, secondary, and tertiary structure.These are formulated as recommendations rather than rules because there is' at present no general agreement about their definition.Note.Two alternative notations are recommended throughout.That with superscripts and subscripts may be used when it is unlikely to cause confusion, e.g., in printed or manuscript material; that without is to be used where superscripts or subscripts may cause confusion or are technically difficult or impossible, e.g., in computer outputs.In the latter connection the following Roman equivalents of Greek