J. Biol. Chem., Vol. 266, Issue 13, 7975-7977, May, 1991

Affinity purification of the photoreceptor cGMP-gated cation channel

R Hurwitz and V Holcombe
Department of Pediatrics and Cell Biology, Baylor College of Medicine, Houston, Texas 77030.

The cGMP-gated cation channel is a member of a new family of channel proteins that appear to be directly regulated by cyclic nucleotides. A protein with a subunit molecular mass of 78 kDa that exhibits cGMP- gated calcium flux when reconstituted into phospholipid-containing vesicles has been purified using 8-bromo-cGMP-agarose affinity chromatography. This channel activity is sensitive to the inhibitor l- cis-diltiazem. Treatment of the reconstituted channel with trypsin abolishes the l-cis-diltiazem sensitivity. Apparent endogenous proteolysis can also result in smaller molecular weight polypeptides that exhibit cGMP-gated channel activity but are insensitive to l-cis- diltiazem. These results show that the channel can bind cGMP and that it contains a l-cis-diltiazem inhibitory domain that is distinct from the cGMP-binding domain.
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