GPCR GPR136, also known as Opsin 5, is a member of the guanine nucleotide binding protein (G protein) coupled receptor superfamily. This gene belongs to the seven exon subfamily of mammalian opsin genes that includes peropsin (RRH) and retinal G protein coupled receptor (RGR). Like these other seven exon opsin genes, this gene may encode a protein with photoisomerase activity. Alternative splicing results in multiple transcript variants encoding different isoforms. ESTs for the GPR136 gene have been identified from human normal testis and B cell/lung/testis libraries..