Abstract
The molecular weight of cattle rhodopsin has been reinvestigated by two independent methods. In the first method rhodopsin preparations, purified in detergent solution by gel filtration and chromatography, respectively, have been analysed for their protein content by quantitative amino acid analysis after hydrolysis and for their retinaldehyde content. This method gives a value of 39 100 ± 900 g protein per mole retinaldehyde for 2 different preparations. The second method, calibrated acrylamide gel electrophoresis in sodium dodecyl sulfate of opsin-free cattle rod outer segment membrane preparations, both before and after enzymatic delipidation, demonstrates the presence of one major band with a molecular weight of 38 600 ± 1000 for 10 preparations. Enzymatically delipidated preparations give the same value, which proves that the presence of lipids does not influence the molecular weight determination by this method. Averaging the results of the two methods, we arrive at a molecular weight of 38 850 ± 900 for the protein part of cattle rhodopsin. Over 85% of the insoluble protein part of cattle rod outer segment membranes appears to consist of rhodopsin protein. Calculation of the molar absorbance at 500 nm of cattle rhodopsin from these data and from measured absorbances, both per mole retinaldehyde and per mole rhodopsin, gives the same result; an average value of 40 300 ± 500. These results confirm that one mole retinaldehyde is present per mole rhodopsin.
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