Abstract
While the action of carboxypeptidase Y on peptides in the presence of an amino acid amide results in transpeptidation products where the C-terminal amino acid residue is exchanged, side products can appear due to condensation reactions. These reactions occur when the peptide is a poor substrate for the enzyme, and hence the competing transpeptidation reaction is very slow. The B-chain of native porcine insulin is such a substrate, and in the presence of H-Thr-NH2 the condensation product (Thr-NH2)B31 insulin is formed together with the transpeptidation product des(Ala)B30(Thr-NH2)B30insulin. The condensation product is only temporarily present in the reaction mixture. It disappears with time in favor of the transpeptidation product. The same reaction pattern is demonstrated for a model compound of insulin Bz-Lys-Ala-OH, and the amount of condensation product is influenced by the reaction conditions: pH, concentration of reactants and solvents. A reaction scheme is proposed to explain the results.
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Abbreviations
- Bz:
-
benzoyl
- Cbz:
-
carbobenzoxy
- CPD-Y:
-
carboxypeptidase Y
- DMF:
-
N,N-dimethylformamide
- DPCC:
-
diphenyl carbamyl chloride
- TEAP:
-
triethylammonium phosphate buffer
- HPLC:
-
high performance liquid chromatography
- INS-Pro-Lys-OH:
-
des(Ala)B30 insulin
- INS-Pro-Lys-Thr-NH2 :
-
des(Ala)B30(Thr-NH2)B30 insulin
References
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Breddam, K., Johansen, J.T. & Ottesen, M. Carboxypeptidase Y catalyzed transpeptidation and condensation reactions. Carlsberg Res. Commun. 49, 457–462 (1984). https://doi.org/10.1007/BF02904398
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DOI: https://doi.org/10.1007/BF02904398