And the alpha subunit, as we'll see, is our G protein. So on a different section of that membrane we have another type of protein that is involved in this activation process. In the secondary messenger system process, this is known as the adenylate cyclase protein. So let's actually take a look and see what happens during our secondary messenger system signal transduction. So basically some type of cell, some type of gland in our body releases this hormone known as epinephrine. Eventually this epinephrine reaches the receptor of that specific cell and that receptor is found on the membrane.