Reversion in expression of hypoxanthine-guanine phosphoribosyltransferase in 6-thioguanine resistant neuroblastoma: Evidence for reduced enzyme levels associated with unaltered catalytic activity

✍ Scribed by Stephen D. Skaper; Elaine B. Spector; J. Edwin Seegmiller

• Book ID: 102880932
• Publisher: John Wiley and Sons
• Year: 1977
• Tongue: English
• Weight: 664 KB
• Volume: 92
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1040920216

✦ Synopsis

Abstract

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 clones 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 K~m~ 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 amount 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.