Stimulation and inhibition of adenylyl cyclases mediated by distinct regulatory proteins

Abstract

Adenylyl cyclases are under positive and negative control by guanine nucleotides and hormones^1–3. Stimulatory responses are mediated by a guanine nucleotide- and Mg-binding regulatory component^4–6 (N_s), a protein that has been purified to homogeneity^7–9. Inhibitory responses have been hypothesized^1–3,10,11 to be mediated by an analogous regulatory component (N_i) distinct from N_s, but definitive proof for this is lacking and these effects may result from modulation of Ns activity. Recently, Bordetella pertussis toxin has been shown¹² to ADP-ribosylate a peptide that is not part of N_s, and this coincides with attenuation of hormonal inhibition of adenylyl cyclase^12–17. We show here that cyc⁻ S49 cells contain a substrate for ADP-ribosylation by pertussis toxin and that the toxin alters GTP dependent inhibition of cyc⁻ adenyl cyclase activity¹⁸. As cyc⁻ S49 cells do not contain N_s by several criteria^5,19–24, we conclude that N_i is a distinct and separate regulatory component of adenylyl cyclase.