Interaction of pyridoxal phosphate with thymidylate synthase: spectral and equilibrium dialysis studies

PLP Induced Inhibition of Thymidylate Synthase Activity in T Lymphocytes

The present study was undertaken in order to examine whether pyridoxine may be used as an inhibitor of thymidylate synthase, and thus, as an antiproliferative agent. It has already been shown by others that pyridoxal phosphate binds thymidylate synthase in vitro. Phytohemagglutinin-stimulated T lymphocytes were cultured in the presence of pyridoxine in various concentrations. Enzyme activity was measured in supernatants of sonicated cell extracts. Our results show that pyridoxine effectively inhibits thymidylate synthase (up to 60–70%) and therefore DNA synthesis (up to 42%) and cell division. We also present evidence that pyridoxine must be phosphorylated to PLP in order to exert its inhibitory effect. Our results suggest that pyridoxal phosphate, in addition to its function as a coenzyme, may have a role in regulating DNA synthesis through modulation of thymidylate synthase activity. Our findings also indicate that pyridoxal phosphate might be tested for its potential immunosuppressive and/or chemotherapeutic action, alone or in combination with other antiproliferative agents.