Phosducin and its isoform fosducyny -like proteins and the recently discovered orphan protein similar to fosducyny , form a distinct group of proteins , which have a function in cytoplasmic regulators phosducin heterotrimeric G protein is highly expressed in the retinal photoreceptor cells , while a much lower concentration , it appears many other cells in certain tissues and lower eukaryotes . This protein can be phosphorylated by the kinase in the dark A -dependent kinase II , and calcium and calmodulin receptor kinases associated with the G protein in its dephosphorylated phosducin mold during light stimulation binds with high affinity to protein subunits bg- G ( Gbg ) . In this way prevents reassociation phosducin bg- subunits of a G - protein subunit ( Ga) and the creation of heterotrimer and acts as a negative regulator of the signal transduction pathway of photoreceptor cells . Substantially similar inhibitory assigned a regulatory mechanism similar to the fosducyny proteins . These observations suggest that phosducin photoreceptor cells plays an important role in the adaptation of these cells to light and dark. Phosducin and its isoforms may also recently been shown to protect against G protein proteasomal destruction , and perhaps also to control transcription factors.