Spermine and spermidine, modulators of the cell surface enzyme adenylate cyclase.

Adenylate cyclase activity was measured in membrane preparations of cultured fibroblasts from 
controls and patients with cystic fibrosis. Enzyme activity increased as the 
transition from exponential growth to confluence occurred; sodium fluoride-stimulated activity more 
markedly displayed this relationship than basal cyclase activity. The in vitro 
addition of spermine (1 X 10(-6) to 2 X 10(-3) M) 
to membrane preparations caused inhibition of basal and sodium fluoride- stimulated 
enzyme activity, with 50% inhibition of basal activity occurring at 10(-6) 
M spermine. Spermidine (10(-4) M) caused 15--25% inhibition of adenylate cyclase 
activity. The increase in fibroblast adenylate cyclase activity during the transition 
from exponential growth was comparable in cells obtained from cystic fibrosis 
patients and control subjects. Basal and sodium-fluoride stimulated adenylate cyclase activity 
as well as inhibition of this enzyme activity by spermidine and 
spermine were undistinguishable between the different cell genotypes. A potential modulation 
of cellular proliferative activity through polyamine interaction with the adenylate cyclase 
system is postulated. 