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Light‐induced activation of the rod phosphodiesterase leads to a rapid transient increase of near‐infrared light scattering
Author(s) -
Paul Kamps K.M.,
Reichert Johannes,
Hofmann Klaus Peter
Publication year - 1985
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(85)80866-8
Subject(s) - transient (computer programming) , infrared , light scattering , phosphodiesterase , chemistry , biophysics , scattering , materials science , optics , physics , biology , biochemistry , enzyme , computer science , operating system
The so‐called AT‐signal described here is a transient light‐induced increase of the near‐infrared scattering from isolated bovine rod outer segments (ROS). Freshly prepared ROS are permeabilized with 0.01% Triton X‐100 immediately before measurement in the presence of 1 mM GTP. The signal amplitude is saturated when ~ 2 rhodopsin molecules out of 30 000 are photo‐excited. The signal recovers rapidly ( ~ 90 s) and can be repeated in a succession of flashes. The AT‐signal can be prevented by pre‐activation of the phosphodiesterase (PDE) enzyme cascade at various levels: either at the level of G‐protein, using ALF 4 − in darkness or GTPγS plus light; or at the level of the PDE catalytic unit, using protamine as an activator. The light sensitivity and kinetics of the AT‐signal are similar to published parameters of PDE activation. These data suggest that light‐induced activation of the PDE is the key reaction for the generation of the signal. On the other hand, blocking of the catalytic cGMP binding site by isobutylmethylxanthine only slightly affects the signal. We propose that the AT‐signal reflects a structural change linked to the transient removal of the PDE inhibitory subunit from the catalytic unit.