The Use of Enzymes for Amino Acid Sequencing

Enzymes are now being used in conjunction with LC-MS to provide sequence information as an alternative to the Edman degradation procedure. 

This is a task for which electrospray ionization is well suited although, as discussed earlier in Section 4.7, this is a soft ionization technique that yields almost exclusively molecular ions with little fragmentation and consequently, in the case of biopolymers, little sequence information directly. 

What is meant by the term MS-MS and what information can it provide What are the advantages of MS-MS over cone-voltage fragmentation (CVF)  

MS-MS is a term that covers a number of techniques in which two stages of mass spectrometry are used to investigate the relationship between ions found in a mass spectrum. In particular, the product-ion scan is used to derive structural information from a molecular ion generated by a soft ionization technique such as electrospray and, as such, is an alternative to CVF. The advantage of the product-ion scan over CVF is that it allows a specific ion to be selected and its fragmentation to be studied in isolation, while CVF bring about the fragmentation of all species in the ion source and this may hinder interpretation of the data obtained. 

A number of enzymes are in common use and each of these cleaves the polypeptide backbone adjacent to a particular amino acid residue. The one used for a particular investigation is therefore chosen for the specificity with which it will cleave the polypeptide backbone of the protein being studied. A number of the enzymes used for this purpose are shown in Table 5.4. 

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