Isolation and Structure of Adenylyl Cyclases

and a cytoplasmic carboxy terminus of ~35 kDa (C2) (FIGURE 1B). The catalytic domain of adenylyl cyclases is hypothesized to be bipartite and split between C1 and C2 regions. The predicted size of mammalian adenylyl cyclases ranges from 110 to 130 kDa, but these proteins generally have an apparent molecular weight on SDS gels of ~200 kDa due to glycosylation in the extracellular loops of M1 and M2. Although the membrane topology and structure of adenylyl cyclases resemble transporters and ion channels, there is no evidence that these enzymes function as transporters or ion channels. However, cultured neurons express a voltage-sensitive adenylyl cyclase activity (25), suggesting that neurons contain an adenylyl cyclase or regulatory protein that is, like some ion channels, sensitive to membrane potential.