Glucagon  TSH   ACTH LH  E@%ephrinc

F---w --+ iYg++     Adenyl Cyclase
                                   -- -

Mg-ATP     cyclic -AMP

Fig. 2:  1969 conceptualization of an adenylyl cyclase system stimulated by
multiple hormones.  Receptors were thought to be separate of adenylyl cyclase
and of having two domains: a distinct ligand binding domain responsible for
specificity of interaction and a common the adenylyl cyclase domain allowing
all to interact with a common enzyme.  (From Rodbell et al., 1970b).