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“Self-screening” of rhodopsin in rod outer segments

1987; Elsevier BV; Volume: 27; Issue: 9 Linguagem: Inglês

10.1016/0042-6989(87)90155-6

1878-5646

Mathew Alpern, Anne B. Fulton, Barbara N. Baker,

Visual perception and processing mechanisms

Microspectrophotometry (MSP) shows rhodopsin highly concentrated (about 3.0mmol/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.