Currently, I am working on the extraction of R-phycocyanin (R-PC) and R-phycoerythrin (R-PE) from red seaweed, Gracilaria tenuistipitata. The powdered seaweed sample was suspended in PBS (pH 7.0) at a ratio of 1:15 (w/v). Following that, I want to separate R-PE from R-PC by ((NH4)2SO4 precipitation. The molecular weight of R-PC and R-PE are 70–110 kDa and 240-260 kDa, respectively. When ((NH4)2SO4 (25% saturation) is added to the crude extract, blue-colored R-PC precipitates first. This is followed by red-colored R-PE precipitation as the concentration of salt increases gradually. However, the scenario should be the reverse as the molecular weight of R-PE is higher than that of R-PC.
In this case, I am seeking suggestions from experts on the appropriateness of my procedure.
If you are able to separate the 2 proteins by the method you are using you should be satisfied. It is not necessarily true that the size of the protein is related to the concentration of ammonium sulfate required to precipitate it.
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