The Journal of General Physiology, Vol 80, 451-472, Copyright © 1982 by The Rockefeller University Press
Euphausiid visual pigments. The rhodopsins of Euphausia superba and Meganyctiphanes norvegica (Crustacea, Euphausiacea)
CJ Denys and PK Brown
The rhabdoms of Euphausia superba contain one digitonin-extractable
rhodopsin, lambda max 485 nm. The rhodopsin undergoes unusual pH- dependent
spectral changes: above neutrality, the absorbance decreases progressively
at 485 nm and rises near 370 nm. This change is reversible and appears to
reflect an equilibrium between a protonated and an unprotonated form of the
rhodopsin Schiff-base linkage. Near neutral pH and at 10 degrees C, the
rhodopsin is partiaLly converted by 420-nm light to a stable 493-nm
metarhodopsin. The metarhodopsin is partially photoconverted to rhodopsin
by long-wavelength light in the absence of NH2OH; in the presence of NH2OH,
it is slowly converted to retinal oxime and opsin. The rhodopsin of
Meganyctiphanes norvegica measured in fresh rhabdoms by
microspectrophotometry has properties very similar to those of the
extracted rhodopsin of E. superba. Its lambda max is 488 nm and it is
partially photoconverted by short wavelength irradiation to a stable
photoconvertible metarhodopsin similar to that of E. superba. In the
presence of light and NH2OH, the M. norvegica metarhodopsin is converted to
retinal oxime and opsin. Our results indicate that previous determinations
of euphausiid rhodopsin absorbance spectra were incorrect because of
accessory pigment contamination.
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