Reduction to 3-Amino Alcohols

A determination of the extra formaldehyde and ammonia produced in this reaction gives an estimation of the number of free a-carboxyl groups, and the residue on which they are located is identified from the nature of the amino alcohol and of the aldehyde R-CHO. Chibnall and Rees have also used this technique to determine the distribution of the protein amide groups between asparagine and glutamine. Residues of aspartic or glutamic acid which have a free oo-carboxyl group are destroyed by the above treatment, while those in amide form remain intact and can be estimated after hydrolysis of the protein. 

At present the only residues to which definite positions in the protein chain can be assigned, are those at or near the terminal positions, and these residues constitute only a small part of the molecule. The position of other residues in the chain can only be determined in the first place relative to one another by the identification of products of partial breakdown. The absolute location of any one residue can be decided only when the relative positions of all the residues are known and when the complete structure of the protein is thus worked out. 

Thus in determining the amino acid sequence of a protein or polypeptide the main task would seem to be to identify as many degradation products as possible. There are essentially two ways of approaching this problem, the first requiring non-specific methods of degradation and the second specific methods. 

This method will generally be applicable to simpler peptides. In the case of larger peptides, the complexity of the mixture will render fractionation difficult and a proportion of larger peptides will be required to work out an unambiguous result. 

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