As with amino acids and peptides, various classes of saponifiable lipids can often be separated by...

As with amino acids and peptides, various classes of saponifiable lipids can often be separated by electrophoresis.

a. Could a mixture of phosphatidylcholine and phosphatidylserine be separated by electrophoresis at pH 7? Explain.

b. At what pH range (from pH 0-14) would it be possible to separate a mixture of phosphatidylcholine and phosphatidylethanolamine by electrophoresis? Explain.

Solutions

Expert Solution

a) It is possible to separate the phosphatidylcholine form the phosphatidylserine at pH= 7, because the choline moiety has a net positive charge, and regard the phosphatidylserine, since the pH = 7 is above its isoelectric point (5.8) of the serine moiety, it will show a negative charge. In presence of the electric current they can be separated by difference of charge. The negative charge of the phosphate is constant in both cases and it is the choline and serine that can do a difference in the total charge.

b) the etanolamine has the moiety o-CH2CH2-NH3 + with a pKa of 10.8. This means that above a pH of 10.8 the ammonium lost the proton. In this case the phosphatidylethanolamine has only the negative charge of the phosphate group. Phosphatidylcholine does not lose its positive charge at any range of pH, but since you need a difference in charge to separate them, above a pH of 10.8 you can separate them.

queen_honey_blossom answered 1 year ago

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