Final answer:
The outcome of activation of a Gi alpha subunit is the inhibition of the adenylyl cyclase/cAMP signaling pathway, leading to a decrease in cAMP levels and downregulation of its effects.
Step-by-step explanation:
When the alpha subunit of a G protein, specifically the Gi alpha subunit, is activated, it often results in the inhibition of the adenylyl cyclase/cAMP signaling cascade. The activation of the Gi alpha subunit leads to a decrease in the levels of cyclic AMP (cAMP) as it inhibits the enzyme adenylyl cyclase, which is responsible for the conversion of ATP to cAMP. Therefore, the activation of this G protein will oppose what happens when Gs alpha subunits activate the adenylyl cyclase, which increases cAMP levels. Since cAMP is a critical secondary messenger involved in signaling pathways, its decrease leads to the inhibition of various downstream effects, including the phosphorylation of proteins by protein kinase A (PKA) and the regulation of gene expression.