INHIBITION OF THYMIDINE KINASE IN GLIAL TUMOR-CELLS BY AN AMINO SUGAR, D-GLUCOSAMINE

  • 1 January 1977
    • journal article
    • research article
    • Vol. 37  (4) , 1068-1074
Abstract
Thymidine kinase activity in rat C6 glioma cells is inhibited by 50-70% after 4 h incubation with 2 mM D-glucosamine. The inhibition is uncompetitive with respect to thymidine, reducing the apparent Km and Vmax of the enzyme. The inhibition does not not appear to be caused by the reversible combination of the enzyme with a cytoplasmic inhibitor, including D-glucosamine and its metabolites. The addition of D-glucosamine or its metabolites to cell free thymidine kinase produced inhibition which differed quantitatively and qualitatively from that which resulted from treatment of intact cells with D-glucosamine. The presence of a reversible cytoplasmic inhibitor of the enzyme was also excluded by mixing experiments. D-Glucosamine inhibited the incorporation of labeled uridine and amino acids into acid precipitable material. The magnitude of inhibition of thymidine kinase activity and amino acid incorporation by D-glucosamine was comparable to that produced by cycloheximide, suggesting that the inhibition might arise from interference with enzyme synthesis. Whereas the kinetics of recovery of amino acid incorporation from inhibition was rapid, thymidine kinase activity was depressed for at least 6 h after drug washout. The results presented are best explained by assuming that 2 forms of thymidine kinase are present in rat C6 cells and are differently affected by D-glucosamine, or D-glucosamine acts by 2 mechanisms to inhibit a single form of the enzyme.