Effect of N-ethylmaleimide on beef and rat liver vitamin K1 epoxide reductase.
There is little difference in the extent of inactivation of beef liver microsomal vitamin K1 epoxide reductase by N-ethylmaleimide (NEM) whether or not the microsomes are pre-treated with dithiothreitol (DTT). The rat liver microsomal enzyme, however, is inactivated by NEM to a much greater extent if the microsomes are pre-treated with DTT. The beef liver enzyme activity is protected from NEM inactivation by the substrate, vitamin K1 epoxide. Ping-pong kinetics are exhibited by the beef liver enzyme. These results support a mechanism for vitamin K1 epoxide reductase in which the function of the required dithiol is to reduce an active site disulfide bond; however, the geometry of the active sites of the enzyme from rat and beef may be different.
Silverman
R B
RB
Department of Chemistry, Northwestern University, Evanston, Illinois 60208.
Nandi
D L
DL
D000818:Animals; D002417:Cattle; D002458:Cell Fractionation / Q000379:methods; D003902:Detergents; D004226:Dithioerythritol / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology*; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors*; D051381:Rats; D064417:Vitamin K Epoxide Reductases
D003902:Detergents; D004226:Dithioerythritol; D006899:Mixed Function Oxygenases; D064417:Vitamin K Epoxide Reductases; D005033:Ethylmaleimide; D004229:Dithiothreitol