The gain of rod phototransduction: Reconciliation of biochemical and electrophysiological measurements

被引:140
作者
Leskov, IB
Klenchin, VA
Handy, JW
Whitlock, GG
Govardovskii, VI
Bownds, MD
Lamb, TD
Pugh, EN
Arshavsky, VY [2 ]
机构
[1] IM Sechenov Evolutionary Physiol & Biochem Inst, St Petersburg 194223, Russia
[2] Harvard Univ, Sch Med, Dept Ophthalmol, Boston, MA 02114 USA
[3] Univ Wisconsin, Mol Biol Lab, Madison, WI 53706 USA
[4] Univ Cambridge, Dept Physiol, Cambridge CB2 3EG, England
[5] Univ Penn, Sch Med, Dept Ophthalmol, Philadelphia, PA 19104 USA
关键词
D O I
10.1016/S0896-6273(00)00063-5
中图分类号
Q189 [神经科学];
学科分类号
071006 ;
摘要
We have resolved a central and long-standing paradox in understanding the amplification of rod phototransduction by making direct measurements of the gains of the underlying enzymatic amplifiers. We find that under optimized conditions a single photoisomerized rhodopsin activates transducin molecules and phosphodiesterase (PDE) catalytic subunits at rates of 120-150/s, much lower than indirect estimates from lightscattering experiments. Further, we measure the Michaelis constant, K-m, of the rod PDE activated by transducin to be 10 mu M, at least 10-fold lower than published estimates. Thus, the gain of cGMP hydrolysis (determined by k(cat)/K-m) is at least 10-fold higher than reported in the literature. Accordingly, our results now provide a quantitative account of the overall gain of the rod cascade in terms of directly measured factors.
引用
收藏
页码:525 / 537
页数:13
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