JBC, Vol. 250, Issue 17, 6897-6903, Sep, 1975
Charge effects in the activation of adenylate cyclase
J. Wolff and G. H. Cook
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.