Evidence for a magnesium dependent ATPase in bovine rod outer segment disk membranes
Uhl, R.; Borys, T.; Abrahamson, E.W.
Photochemistry and Photobiology 29(4): 703-706
1979
ISSN/ISBN: 0031-8655 PMID: 156376 DOI: 10.1111/j.1751-1097.1979.tb07753.x
Accession: 040076714
Abstract- In the presence of Mg2+ 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'. Ca2+ cannot replace Mg2+. 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 Mg2+ 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'.
