Number of rhodopsin molecules in rod photoreceptor cell

Range toad ~3×10^9: mammal ~10^8 rhodopsins/rod
Organism vertebrates
Reference F. Rieke and D. A. Baylor, Single-photon detection by rod cells of the retina, Rev. Mod. Phys. 70, 1027 – Published 1 July 1998 DOI: link p.1033 left column bottom paragraph
Comments “There are two primary components of the cellular dark noise, each of which contributes about equally to the total variance of the dark current (Baylor, Matthews, and Yau, 1980). One component consists of occasional discrete events that resemble single-photon responses [arrows in Fig. 6(a)]. These events originate from thermal isomerization of rhodopsin and occur about once every 30 sec in a toad rod at 20°C (Baylor, Matthews, and Yau, 1980) and about once every 90 sec in a mammalian rod at 37°C (Baylor, Nunn, and Schnapf, 1984). The toad rod contains about 3×10^9 rhodopsin molecules, so each rhodopsin activates spontaneously only once every few thousand years-the mammalian rod contains about 10^8 rhodopsins, each of which activates spontaneously about once every 300 years at 37°C.”
Entered by Uri M
ID 111344