Inactivation of the Na, K-ATPase by radiation-induced free radicals. Evidence for a radical-chain mechanism.
Free radicals produced by water radiolysis were used to study the inactivation of the enzymatic activity of the Na,K-ATPase. A decrease of the activity to virtually zero with a mono-exponential dependence on the radiation dose was observed. The inactivation process is initiated by hydroxyl radicals. This was shown by the effect of appropriate radical scavengers such as t-butanol, formate and vitamin C. In all cases a significant increase in the characteristic D37 dose of inactivation was observed. Inactivation was found to show a so-called inverse dose-rate effect, i.e., the sensitivity of the enzyme to radical attack is increased if the dose rate is reduced. The data were found to agree with the relationship 1/D37 approximately 1/D1/2, which is known to be a strong indicator of a radical chain mechanism. This means that the inactivation, after initiation by single radicals, is amplified by a subsequent chain mechanism.
Department of Biology, University of Konstanz, Germany.
K
K
Hitschke
R
R
Bühler
H J
HJ
Apell
G
G
Stark
D002462:Cell Membrane / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D016166:Free Radical Scavengers; D017665:Hydroxyl Radical / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D014867:Water
D016166:Free Radical Scavengers; D014867:Water; D017665:Hydroxyl Radical; D000254:Sodium-Potassium-Exchanging ATPase