Measurement of isoelectric points of phospholipid exchange proteins by gel isoelectric focusing.

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Abstract
A method of estimating the isoelectric points of phospholipid exchange proteins is described. The phospholipid presumably bound to a phospholipid exchange protein was replaced with [3H]phosphatidylcholine of a high specific radioactivity by an incubation of the protein with liposomes containing the labeled lipid and dimannosyl diglyceride. After incubation, a major portion of the liposomes was separated from the protein by an affinity of liposomes to concanavalin A-Sepharose 2B. The isoelectric point of the protein was measured by gel isoelectric focusing and was located by tritium radioactivity of the bound [3H]phosphatidylcholine. The method was used to measure isoelectric points of partially purified phospholipid exchange proteins in pig liver.