cGMP is activated by nitric oxide by interacting with the heme group of the enzyme soluble guanylate cyclase (sGC). This interaction between the two allows sGC to convert GTP into cGMP. This process is known as the NO/cGMP signaling pathway. This pathway is involved in several processes such as the regulation of muscle relaxation, neurotransmission, and hormonal secretion. Once cGMP is produced, it may activate protein kinase G, which leads to activation of myosin phosphate. This in turn leads to the release of calcium from intracellular stores in smooth muscle cells.