Phospholipid exchange proteins in rat intestine.

The 105,000 g supernatant and pH 5.1 supernatant fractions from rat intestinal homogenates stimulate phosphatidylcholine exchange between [32P] phosphatidylcholine liposomes and beef heart mitochondria. This active fraction shows the characteristics of a protein. Isoelectric focusing of the intestinal pH 5.1 fraction shows two peaks of phosphatidylcholine exchange activity: one at an acidic pH (4.5-5.3), the other in a basic pH range (8-9). The second peak of activity appears to be a new phospholipid exchange protein. The anatomic distribution of phosphatidylcholine exchange activity in intestine has been investigated. Expressed per mg of protein, phosphatidylcholine exchange activity is higher in mucosa than in the intestinal wall. No significant differences have been found between villi and crypts cells or between jejunal and ileal villi. Futhermore, exchange activity per mg of protein in mucosa is unaffected by fasting or by feeding a high fat or high cholesterol diet. This suggests that phospholipid exchange activity in the absorptive cells is not a rate limiting step in the process of fat absorption.