Membrane SH-groups related to adrenaline action in rat adipocytes: a comparative study using sulfhydryl reagents of different molecular size.

The orientation of SH-groups within the fat cell membrane involved in adrenaline (and NaF) action was studied by comparing the effects of uncoupled p-CMB with those of a large derivative of this reagent -- p-CMB-dextran --. Preincubation of intact adipocytes with uncoupled p-CMB caused a dose-dependent inhibition of adrenaline (and NaF) stimulated adenylate cyclase activity as determined in ghosts prepared subsequently. Preincubation with p-CMB-dextran, however, influenced neither the lipolytic response to adrenaline nor the catecholamine (and NaF) activated adenylate cyclase activity. When p-CMB-dextran was present during ghost preparation, a dose-dependent inhibition of adrenaline (and NaF) stimulated adenylate cyclase activity was observed. These results suggest that the binding sites of adrenaline as well as SH-groups essential for activity of adenylate cyclase are not localized near enough to the exterior surface to be accessible for p-CMB-dextran. The polarity in the sensitivity of fat cell adenylate cyclase could not be observed when p-CMB-dextran was added directly to intact or fragmented ghosts. The abbreviations used are: Cyclic AMP, cyclic adenosine 3',5'-monophosphate; p-CMB, p-chloromercuribenzoate.