"Self-screening" of rhodopsin in rod outer segments.
Microspectrophotometry (MSP) shows rhodopsin highly concentrated (about 3.0 mmol/l) in rod outer segments (ROS). Calculation of the in vivo absorption spectrum of human rhodopsin from such data reveals a striking failure to agree with the action spectrum of human rod vision. Agreement is good between the spectral distribution of absorption coefficients and the action spectrum, but the "concentration-broadening" (or "self-screening") introduced by the high end on absorbance at this concentration results in a misfit among the largest in the 93 years comparisons of this kind have been made! To deal with this anomaly, it has been suggested that "concentration-broadening" is inappropriate for rhodopsin in rod vision. This proposal was tested by comparing rod action spectra of 15-day-old and adult rats, since the lengths of ROS increase by a factor of about two in maturation. Three lines of evidence are inconsistent with it. Although the conundrum remains unexplained, it cannot be dismissed by supposing "self-screening" inappropriate for night vision.
Alpern
M
M
Vision Research Laboratory, W.K. Kellogg Eye Center, University of Michigan, Ann Arbor 48105.
Fulton
A B
AB
Baker
B N
BN
D000375:Aging / Q000502:physiology; D000818:Animals; D003623:Dark Adaptation; D004596:Electroretinography; D008027:Light; D010786:Photoreceptor Cells / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012168:Retinal Pigments / Q000502:physiology*; D012243:Rhodopsin / Q000502:physiology*; D012374:Rod Cell Outer Segment / Q000502:physiology*; D013053:Spectrophotometry
D012168:Retinal Pigments; D012243:Rhodopsin