Genetics of Eye Diseases by Chitra Kannabiran

Author:Chitra Kannabiran
Language: eng
Format: epub
ISBN: 9789811371462
Publisher: Springer Singapore

5.3.2 Phosphodiesterase 6

The phosphodiesterase 6 enzyme is involved in hydrolysis of cGMP in the photoreceptors during the transduction of light signals. The hydrolysis of cGMP by this enzyme in response to light leads to a fall in cGMP levels in the photoreceptor. Thus the cGMP-gated sodium ion channels (known as cyclic nucleotide gated channels (CNGC)) on the outer segment membranes close due to fall of cGMP levels. This process arrests the influx of sodium ions into the cells and thus results in hyperpolarization of the outer segment (i.e., the membrane becomes more negative, with a potential of −65 mV). In the dark, the photoreceptor cells are depolarized and have a potential of around −40 mV. Phosphodiesterase 6 has three types of subunits, two large alpha and beta subunits and two small gamma subunits; each of the three subunits is encoded by a separate gene, PDE6A, PDE6B, and PDE6G, respectively. It is thus a heteromeric enzyme, and the subunits α, β, and Ƴ are about 88 kDa, 84 kDa, and 10 kDa, respectively, in the bovine protein.

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