Protein synthesis using peptide fragments

Protein Synthesis using Peptide Fragments Derived from Solid Phase Peptide Synthesis... 

The stepwise solution-synthesis procedure has been successfully employed for the synthesis of peptides. Its applicability was demonstrated in a synthesis of oxytocin. l A few larger peptides have been synthesized in solution entirely by this strategy, a notable example being the synthesis of secretin, a 27 amino acid residue peptide.f °l Another use of this strategy is for the preparation of peptide fragments as building blocks of larger peptides and proteins. 

The proteasome and other proteases generate free amino acids. Ubiquitinated proteins are processed to peptide fragments from which the ubiquitin is subsequently removed and recycled. The peptide fragments are further digested to yield free amino acids, which can be used for biosynthetic reactions, most notably protein synthesis. Alternatively, the aminO group can be removed and processed to urea (p. 661) and the carbon skeleton can be used to synthesize carbohydrate or fats or used directly as a fuel for cellular respiration. 

Although, in principal it is possible to perform totally enzymatic synthesis of peptides, in practice combined chemical and enzymatic steps are preferred. For the classical enzymochemical synthesis of polypeptides and even small proteins, the optimum approach is usually synthesis of fragments using the SPPS methodology... 

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