Loss of a thermolabile thymidine kinase activity in bromodeoxyuridine resistant (transport deficient, kinase positive) haploid cultured frog cells

Journal Article · Thu Jan 01 04:00:00 EST 1976 · Exp. Cell Res.; (United States)

DOI:https://doi.org/10.1016/0014-4827(76)90687-X· OSTI ID:7256582

Freed, J J; Hames, I M

Haploid frog cell strain ICR B20 is resistant to 10/sup -4/ M bromodeoxyuridine through its failure to express a thymidine-specific saturable transport reaction, although it continues to express thymidine kinase (EC 2.7.1.75) at levels comparable to that of the sensitive parental strain ICR 2A. However, the thymidine kinases of these two lines are not entirely equivalent: we report here that ICR 2A enzyme appears to contain two fractions of differing thermostability and that ICR B20 expresses only the more thermostable form. Plots of log surviving enzyme activity vs time at 45/sup 0/C from ICR 2A are biphasic and may be resolved into a thermolabile component F with a half-life about 5 min and a thermostable component S with a half-life greater than 200 min. Similar plots from ICR B20 are exponential and indicate a half-life greater than 200 min. The fraction of the initial enzyme activity represented by F averages about one-third of the total. If ICR 2A enzyme is heated in the presence of thymidine (0.05 mM), component F is stabilized. However, dialysis against thymidine-free buffer does not make S activity thermolabile. The time course of enzyme reaction in ICR 2A preparations in non-linear and suggests that F activity may decay independently of S; ICR B20 extracts (and extracts of ICR 2A that have previously been heated at 45/sup 0/C) give nearly linear reaction rates. These observations suggest that the transport deficiency of ICR B20 is associated with loss of a portion of the total thymidine kinase activity and raise the possibility that the lost fraction of activity may participate in transport.

• Research Organization: Inst. for Cancer Research, Philadelphia
• OSTI ID: 7256582
• Journal Information: Exp. Cell Res.; (United States), Journal Name: Exp. Cell Res.; (United States) Vol. 99; ISSN ECREA
• Country of Publication: United States
• Language: English

Related Subjects

550500* -- Metabolism
59 BASIC BIOLOGICAL SCIENCES
AMPHIBIANS
ANIMAL CELLS
ANIMALS
ANTIMETABOLITES
ANTIMITOTIC DRUGS
AQUATIC ORGANISMS
AZINES
BIOLOGICAL EFFECTS
BROMOURACILS
BUDR
CELL CULTURES
DRUGS
ENZYMES
FROGS
HAPLOIDY
HETEROCYCLIC COMPOUNDS
HYDROXY COMPOUNDS
METABOLISM
NUCLEOSIDES
NUCLEOTIDES
ORGANIC BROMINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOSPHOTRANSFERASES
PLOIDY
PYRIMIDINES
RIBOSIDES
TEMPERATURE DEPENDENCE
THYMIDINE
TRANSFERASES
URACILS
VERTEBRATES