<P> Protein sequencing is the practical process of determining the amino acid sequence of all or part of a protein or peptide . This may serve to identify the protein or characterize its post-translational modifications . Typically, partial sequencing of a protein provides sufficient information (one or more sequence tags) to identify it with reference to databases of protein sequences derived from the conceptual translation of genes . </P> <P> The two major direct methods of protein sequencing are mass spectrometry and Edman degradation using a protein sequenator (sequencer). Mass spectrometry methods are now the most widely used for protein sequencing and identification but Edman degradation remains a valuable tool for characterizing a protein's N - terminus . </P> <P> It is often desirable to know the unordered amino acid composition of a protein prior to attempting to find the ordered sequence, as this knowledge can be used to facilitate the discovery of errors in the sequencing process or to distinguish between ambiguous results . Knowledge of the frequency of certain amino acids may also be used to choose which protease to use for digestion of the protein . The misincorporation of low levels of non-standard amino acids (e.g. norleucine) into proteins may also be determined . A generalized method often referred to as amino acid analysis for determining amino acid frequency is as follows: </P>

How to identify amino acid sequence of a protein