Figure 1.

The complex interrelationship between the effects of changing the concentrations of adenosine triphosphate (ATP) and Mg on adenylyl cyclase activity in the absence and presence of saturating adrenocorticotropic hormone (ACTH) or 10 mM NaF (A) reveals that hormonal and fluoride stimulation shift the requirement toward lower concentrations without affecting the apparent cooperative nature of the dependence on Mg (B). Adapted from ref. 1.