CONTROL OF PHOTORECEPTOR PROTEINS BY CA2+

A decrease of cytoplasmic Ca2+-concentration in vertebrate photorecept or cells after illumination is necessary for light adaptation. Althoug h the mechanisms of adaptation is not completely understood, several C a2+-dependent cellular processes have been discovered, Some involve ca lcium-binding proteins like recoverin, guanylyl cyclase-activating pro tein and calmodulin, and their target proteins rhodopsin kinase, guany lyl cyclase, the cGMP-gated channel, and NO synthase, The activity of several enzymes or channels Is directly controlled by Ca2+ and does no t involve calcium-binding proteins, These proteins are pyrophosphatase , protein kinase C and the cGMP-gated channel.