Martignoni M, Benedetti M, Davey GP, Tipton KF, McDonald AG. Degradation of thymic humoral factor γ2 in human, rat and mouse blood: An experimental and theoretical study.
BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2020;
1868:140467. [PMID:
32512181 PMCID:
PMC7274130 DOI:
10.1016/j.bbapap.2020.140467]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Revised: 05/12/2020] [Accepted: 06/03/2020] [Indexed: 11/28/2022]
Abstract
The degradation of the immunomodulatory octapeptide, thymic humoral factor γ2 (THF-γ2, thymoctonan) has been studied in whole blood samples from human, rat and mouse. The peptide, Leu-Glu-Asp-Gly-Pro-Lys-Phe-Leu, was shown to be rapidly degraded by peptidases. The half-life of the intact peptide was less than 6 min at 37 °C in blood from the three species tested. The main fragments formed from THF-γ2 were found to be Glu-Asp-Gly-Pro-Lys-Phe-Leu (2–8), Asp-Gly-Pro-Lys-Phe-Leu (3–8) and Glu-Asp-Gly-Pro-Lys (2–6) in human and in rat blood and 2–8 and 2–6 in mouse blood. Analysis of the time course of degradation revealed a sequential removal of single amino acids from the N-terminus (aminopeptidase activities) in a process that was apparently unable to cleave the Gly-Pro bond (positions 4–5 in the peptide) together with an independent cleavage of the Lys-Phe bond (positions 6–7 in the peptide) to release the dipeptide Phe-Leu. This behaviour and the effects of inhibitors showed the involvement of metallo-exopeptidases in the N-terminal digestion and a phosphoramidon-sensitive metallo-endopeptidase in the cleavage of the Lys-Phe bond. The degradation patterns in human blood were modelled in terms of the competing pathways involved approximating to first-order kinetics, and an analytical solution obtained via the method of Laplace Transforms. The half-life of THF degradation in whole rat blood sample was found to be significantly lower than in human or mouse.
The immunomodulatory octapeptide THF-γ2 is rapidly degraded in human and rodent blood.
The half-life of the intact peptide was <6 min in all species.
The nature of the peptidases involved was determined by the use of specific inhibitors.
Laplace transforms were used to model the degradation patterns in human blood.
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