Reversion in expression of hypoxanthine-guanine phosphoribosyltransferase in 6-thioguanine resistant neuroblastoma: evidence for reduced enzyme levels associated with unaltered catalytic activity.
Five clones of mouse neuroblastoma cells able to grow in hypoxanthine-aminopterin-thymidine containing medium were isolated from a hypoxanthine-guanine phosphoribosyltransferase (HGPRT; EC 2.4.2.8; IMP: pyrophosphate phosphoribosyltransferase) deficient cell line. These hypoxanthine-aminopterin-thymidine resistant revertant clone had 45-55% of wild-type cell HGPRT activity. Kinetic studies indicated that the HGPRT in revertant clones had a reduced maximal velocity as compared to wild type cells based on cell protein. Apparent Km values of HGPRT for hypoxanthine and 5-phosphoribosyl-1-pyrophosphate were similar in wild-type and revertant cells. Heat inactivation studies demonstrated a similar heat lability for HGPRT in revertant and wild-type cells. An antibody fraction prepared from serum of rabbits immunized with HGPRT partially purified from mouse liver was used to measure the amount of cross-reacting material in normal and revertant clones. The revertant clones had one-half the amounth of cross-reacting material present in wild-type cells, based on a given amount of cell protein. These data indicate that the revertant cells may contain fewer HGPRT molecules with unaltered catalytic activity.
D000228:Adenine Phosphoribosyltransferase / Q000378:metabolism; D002460:Cell Line; D004351:Drug Resistance; D004591:Electrophoresis, Polyacrylamide Gel; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007041:Hypoxanthine Phosphoribosyltransferase / Q000276:immunology / Q000378:metabolism*; D007118:Immunoassay; D007700:Kinetics; D009154:Mutation; D009447:Neuroblastoma / Q000201:enzymology; D010754:Phosphoribosyl Pyrophosphate / Q000378:metabolism; D013866:Thioguanine / Q000494:pharmacology
D010754:Phosphoribosyl Pyrophosphate; D000228:Adenine Phosphoribosyltransferase; D007041:Hypoxanthine Phosphoribosyltransferase; D013866:Thioguanine