Stabilization of lipoprotein lipase by endothelial cells

Lipoprotein lipase, purified from bovine milk, lost 90% of its activity when incubated in Hanks' balanced salt solution for 5 min at 37 degrees C. Bovine pulmonary artery endothelial cells, maintained in culture, markedly stabilized this enzyme. The stabilizing factor of endothelial cells was non-dialyzable, resistant to heating at 100 degrees C and to changes in pH, and unaffected by treatments of cells with proteolytic enzymes or with heparinase (Flavobacterium heparinum enzyme). However, the stabilizing effect on lipoprotein lipase was reduced by 60-70% by the extraction of cells with chloroform/methanol (2:1). The lipid extract of the cells stabilized the enzyme, suggesting that lipid component(s) of the endothelial cells account for their stabilizing effect. Since the endothelial cell is thought to be the site of action of lipoprotein lipase, stabilization of the enzyme by this cell may play a role in its preservation and function in vivo.