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EVIDENCE FOR A MAGNESIUM DEPENDENT ATPase IN BOVINE ROD OUTER SEGMENT DISK MEMBRANES*†
Author(s) -
Uhl Rainer,
Borys Tom,
Abrahamson Edwin W.
Publication year - 1979
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1979.tb07753.x
Subject(s) - rhodopsin , gtp' , atp hydrolysis , guanosine , adenosine triphosphate , guanosine triphosphate , atpase , biophysics , chemistry , membrane , transduction (biophysics) , visual phototransduction , biochemistry , retinal , enzyme , biology
Abstract—In the presence of Mg 2+ and adenosine triphosphate (ATP), a rapid. light‐induced, light‐scattering transient is observed from bovine rod outer segments (ROS). This light‐scattering transient we have labelled ‘A’. Ca 2+ cannot replace Mg 2+ . nor can guanosine triphosphate (GTP) replace ATP. ‘A’ is observed at ATP concentrations as low as a few μM. The half‐time of ‘A’, 60 ms at 20° and 20 ms at 37°, is consistent with a process possibly involved in visual transduction. ‘A’ has the action spectrum of rhodopsin bleaching and its amplitude is strictly proportional to the fraction of rhodopsin bleached per flash. ‘A’ can be regenerated by 11‐ cis retinal. Inhibition studics with ATP analogues, which cannot be hydrolysed and fail to evoke an ‘A’ response, reveal that an ATP hydrolysis process has to precede illumination in order for ‘A’ to occur. On the basis of the above findings. it is proposed that there is a Mg 2+ dependent ATPase in ROS that allows the disk membrane to assume a new membrane state which, upon illumination, is altered. giving rise to the structural phenomenon monitored as light‐scattering transient ‘A’.