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

Ilya B. Leskov, Vadim A. Klenchin, Jason W. Handy, Gary G. Whitlock, Viktor I. Govardovskii, M. Deric Bownds, Trevor D. Lamb, Edward N Pugh Jr, Vadim Y. Arshavsky

Research output: Contribution to journalArticlepeer-review

145 Scopus citations

Abstract

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 light-scattering experiments. Further, we measure the Michaelis constant, K(m), of the rod PDE activated by transducin to be 10 μM, 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.

Original languageEnglish (US)
Pages (from-to)525-537
Number of pages13
JournalNeuron
Volume27
Issue number3
StatePublished - 2000
Externally publishedYes

ASJC Scopus subject areas

  • Neuroscience(all)

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