PED6H is the inhibitory (or gamma) subunit of the cone-specific cGMP phosphodiesterase, which is a tetramer composed of two catalytic chains (alpha and beta), and two inhibitory chains (gamma). It is specifically expressed in the retina, and is involved in the transmission and amplification of the visual signal. Mutations in this gene are associated with retinal cone dystrophy type 3A (RCD3A). Recombinant human PED6H protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.