Sequencing, proteins chemical cleavage

The separation of the target protein from the fusion protein can be performed chemically or enzymatically. The basis for chemical cleavage is acid or base stability of the target protein. Enzymatic separation by proteases is highly specific but its efficiency can be decreased by limited access to the part of the amino acid sequence required for proteolysis. 

Since the fusion protein partner is substantially larger than the size of the required peptide, overall peptide yield represents only a fraction of the purified fusion protein, even before losses due to subsequent purification. For example, for a fusion protein of 150 amino acids and a peptide of 15 amino acids, the relative levels of products are 91 and 9%, respectively. So, it is useful to increase the proportion of the final fusion protein that comprises peptide sequences. This can be achieved either by using a smaller fusion protein or by increasing the number of peptide sequences cloned in tandem with the fusion partner. As shown in the following examples both approaches have been adopted, but with variable results. Finally, the separation of the tandem repeats of peptides into monomers can be achieved by either chemical cleavage or enzymatic cleavage (Section 1.1.1.3). 

When sequencing proteins, one tries to generate overlapping peptides by using cleavages at specific sites. Which of the following statements about the cleavages caused by particular chemicals or enzymes are true ... 

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