Thymoctonan

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.

Using matrix to enhance the molecular ion signals for biomolecule identification without loss of spatial resolution caused by matrix crystallization is a great challenge for the application of TOF-SIMS in real-world biological research. In this report, graphene oxide (GO) was used as a matrix for TOF-SIMS to improve the secondary ion yields of intact molecular ions ([M + H]⁺). Identifying and distinguishing the molecular ions of lipids (m/z >700) therefore became straightforward. The spatial resolution of TOF-SIMS imaging could also be improved as GO can form a homogeneous layer of matrix instead of crystalline domain, which prevents high spatial resolution in TOF-SIMS imaging. Lipid mapping in presence of GO revealed the delicate morphology and distribution of single vesicles with a diameter of 800 nm. On GO matrix, the vesicles with similar shape but different chemical composition could be distinguished using molecular ions. This novel matrix holds potentials in such applications as the analysis and imaging of complex biological samples by TOF-SIMS. Graphical Abstract ᅟ.