Charge effects in the activation of adenylate cyclase

Abstract

Polycations, including ribonuclease A, ribonuclease S protein and peptide, spermine, spermidine, and polylysines, enhance unstimulated and stimulated adenylate cyclase activity of beef thyroid membranes at low concentrations and inhibit these activities at high concentrations. Peak polylysine stimulation occurs with degrees of polymerization of 6 to 14, and for large polymers a potency limit for this maximum is reached at 4 X 10(-5) M expressed as lysine residues. Both enhancement and inhibition appear to be due to charge-charge interactions and are abolished by KC1. Polyanions are inhibitory only. The biphasic effect of polycations is seen on basal cyclase activity, occurs with prostaglandin E1- and 5'-guanylyl-imidodiphosphate-stimulated cyclase, but is most striking with thyrotropin. There is little enhancement of F--activated cyclase. The enhancement is not sensitive to changes in pH, Mg2+, or regenerating system and does not correlate with the stability constants between polycations and ATP. We suggest that the polycation effect is a general, electrostatic effect on membrane conformation and is not restricted to a particular receptor domain.