Phospholipid transfer activities in morris hepatomas and the specific contribution of the phosphatidylcholine exchange protein

Abstract

Phospholipid transfer activities for phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine were measured in three hepatomas of increasing growth rate and degree of dedifferentiation, the hepatomas 7787, 9633 and 7777, and compared to the activities found in normal and host liver. A 2–3-fold increase was found in the phosphatidylcholine and phosphatidyinositol transfer activities in the fast-growing 7777 hepatoma, while these activities were moderately or not increased in the 7787 and 9633 hepatomas. Phosphatidylethanolamine transfer was found to be extremely low in all three hepatomas. The possible significance of these findings with respect to the altered phospholipid content and composition of the hepatoma membranes is discussed.

The contribution of the phosphatidylcholine specific exchange protein to the total phosphatidylcholine transfer activity was determined in normal and host liver and in the hepatomas 7777 and 9633 with the aid of a phosphatidylcholine exchange protein specific antiserum. To this end a new procedure for the purification of the phosphatidylcholine exchange protein from rat liver was developed which leads to a final purification factor of 5300 and a high overall yield of 17%. In addition, this protein was chemically and immunologically characterized and its properties were compared to those of the bovine phosphatidylcholine exchange protein purified in our laboratory previously.