TYMS and cancer: Theory and experimental data indicate that increase of the cytotoxic activity of FUra depends to a still undetermined limit on the level of intracellular expansion of PLP pools to enhance the SHMT-catalyzed synthesis of CH2-H4PteGlu within cancer cells exposed to FdUMP and reduced folate in a time range permitting sustained inhibition of the TS through stabilization of the ternary complex [TS-FdUMP-5,10-CH2-H4PteGlu] by enhancement of CH2-H4PteGlu mass flux.