Effect of cadmium on purified hepatic flavokinase: involvement of reactive -SH group(s) in the inactivation of flavokinase by cadmium.
The effect of cadmium (Cd2+) was studied in vitro on the flavokinase (ATP : riboflavin 5'-phosphotransferase, EC 2.7.1.26) activity purified from rat liver. Cadmium inhibited flavokinase activity in a concentration-dependent manner and the effect was completely reversed by increasing concentration of zinc (Zn2+), indicating a competition between Zn2+ and Cd2+ for binding with the enzyme. Further, a competition between riboflavin and Cd2+ hints at the possibility that Zn2+ and Cd2+ probably compete for the same site on the enzyme where riboflavin binds. Our studies further reveal that hepatic flavokinase contains essential, accessible and functional thiol group(s) as evidenced by a concentration-dependent inhibition by sulfhydryl reagents and protection by thiol protectors like glutathione or dithiothreitol. Furthermore, the enzyme could also be protected from the inhibitory effect of Cd2+ and Hg2+ by glutathione and dithiothreitol suggesting that Cd2+ probably interacts with reactive thiol group at or near the active site of the enzyme to cause inhibition.
Bandyopadhyay
D
D
Indian Institute of Chemical Biology, Calcutta.
Chatterjee
A K
AK
Datta
A G
AG
D000818:Animals; D001665:Binding Sites; D002104:Cadmium / Q000494:pharmacology*; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D005033:Ethylmaleimide / Q000494:pharmacology; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors* / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats; D013439:Sulfhydryl Reagents / Q000378:metabolism*
D013439:Sulfhydryl Reagents; D002104:Cadmium; D004228:Dithionitrobenzoic Acid; D017853:Phosphotransferases (Alcohol Group Acceptor); C022532:riboflavin kinase; D005033:Ethylmaleimide