Guanine nucleotides and adenosine "R(i)'-site analogues stimulate the membrane-bound low-K(m) cyclic AMP phosphodiesterase of rat adipocytes.

Concentrations of GTP or Gpp(NH)p up to 300 nM activated the membrane-bound low-K(m) cyclic AMP phosphodiesterase of rat adipocytes, while higher concentrations of these nucleotides reversed this activation. The adenosine analog N6-phenylisopropyladenosine (N6-PIA) elicited a dose-dependent stimulation of this enzyme (K(act) = 3 nM), an effect which did not require GTP and which was additive with the GTP-induced stimulation. Both the N6-PIA and GTP stimulations were rapid, reversible and resulted from an increase in V(max). In contrast, neither GTP, nor N6-PIA affected the soluble low-K(m) cyclic AMP phosphodiesterase.