Abstract
The importance of the phospholipids present in cattle rod outer segments for the spectral integrity of rhodopsin was studied. The molar ratio of lipid phosphorus to retinaldehyde bound in rhodopsin could be reduced from 87 to 4 by means of treatment with phospholipase C from Bacillus cereus without affecting the spectral integrity of the rhodopsin. Hexane extraction of the phospholipase C-treated material did not further reduce the lipid phosphorus to retinaldehyde ratio, but did remove diglycerides arising from the hydrolyzed phospholipids. The photolytic properties of phosphlipase C-treated rhodopsin remained intact also during the hexane extraction. From this it was concluded that neither the polar moiety nor the diglyceride part of 95% of the phospholipids in the rod outer segments are essential for the spectral integrity of rhodopsin. Quantitative analysis of the phospholipids present in the phospholipase C-treated, hexane-extracted preparation showed that they consisted of 1.6 mole phosphatidyl serine, 0.4 mole diphosphatidyl glycerol, 0.6 mole sphingomyeline, and 0.1 mole phosphatidyl ethanolamine per mole of retinaldehyde. These findings rule out the possibility that the retinaldehyde group in rhodopsin is linked to phosphatidyl ethanolamine.
Published Version
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