Photoactivated adenylyl cyclase (PAC) was discovered in "Euglena gracilis" and can be expressed in other organisms through genetic manipulation. Shining blue light on a cell containing PAC activates it and abruptly increases the rate of conversion of ATP to cAMP. This is a useful technique for researchers in neuroscience because it allows them to quickly increase the intracellular cAMP levels in particular neurons, and to study the effect of that increase in neural activity on the behavior of the organism. A green-light activated rhodopsin adenylyl cyclase (CaRhAC) has recently been engineered by modifying the nuclecotide binding pocket of rhodopsin guanylyl cyclase.