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Rod Outer Segment Structure Influences The Apparent Kinetic Parameters Of Cyclic Gmp Phosphodiesterase, Charles Dumke, Vadim Y. Arshavsky, Peter D. Calvert, M. Deric Bownds, Endward N. Pugh Jr.

Integrative Physiology and Athletic Training Faculty Publications

Cyclic GMP hydrolysis by the phosphodiesterase (PDE) of retinal rod outer segments (ROS) is a key amplification step in phototransduction. Definitive estimates of the turnover number, kcat, and of the Km are crucial to quantifying the amplification contributed by the PDE. Published estimates for these kinetic parameters vary widely; moreover, light-dependent changes in the Km of PDE have been reported. The experiments and analyses reported here account for most observed variations in apparent Km, and they lead to definitive estimates of the intrinsic kinetic parameters in amphibian rods. We first obtained a new and highly accurate estimate of the ratio …