CATABOLISM OF THE TETRAPEPTIDE N-AC-SER-ASP-LYS-PRO (ACSDKP), AN INHIBITOR OF HEMATOPOIETIC STEM-CELL (CFU-S) PROLIFERATION, FOLLOWING INVITRO INCUBATION WITH HEMATOPOIETIC TISSUES FROM NORMAL AND LEUKEMIC MICE

The comparative degradation of N-Ac-Ser-Asp-Lys-Pro (AcSDKP), a negati ve regulator controlling the proliferation of the hematopoietic plurip otent stem cell, was investigated following incubation with plasma, bo ne marrow and spleen cells from normal mice and mice bearing a transpl antable myeloid leukemia. Using the tetrapeptide, specifically radiola belled in the lysyl residue, degradation of [H-3]AcSDKP was followed b y measurement of [H-3]Lys formation resulting from its catabolism. It was shown that already after 1 h the degradation of AcSDKP in plasma f rom leukemic mice was higher compared to that following incubation in plasma from normal mice, whereas incubation with bone marrow cells exh ibits a small difference only after 4 hours incubation. However, no in crease of AcSDKP catabolic activity was observed following incubation with spleen cells from leukemic animals when compared with incubation of normal spleen cells.