Inhibition by N-ethylmaleimide of the epinephrine-induced phosphorylase and lipolysis activation

Abstract

The effect of N-ethylmaleimide (NEM) on the epinephrine-induced activation of phosphorylase in diaphragm and that of lipolysis in epididymal fat pad in male rats was examined. When the isolated diaphragm was preincubated with NEW, 1 mM, epinephrine could not activate the phosphorylase. The activation of phosphorylase b kinase was also inhibited by the preincubation with NEM. The partially purified phosphorylase b kinase preparation was more rapidly inactivated by NEM than phosphorylase b crystals. The activation of lipolysis by in vitro epinephrine in adipose tissue or isolated fat cells was blocked by NEM or SH-blocking agents. The effect of ACTH was also inhibited by NEM. The inhibitory effect of NEM was not restored by the addition of glutathione 10 seconds after the fat cells were contacted with NEM. Thus, NEM probably changes the quality of tissue to block the action of epinephrine.