Heparin-modulated Binding of Pancreatic Lipase and Uptake of Hydrolyzed Triglycerides in the Intestine

Utilizing small intestine membranes that contain heparin (50 µg/mg protein), binding of triglyceride lipase (homogeneous 52 kDa, specific activity, 70 nmol/mg·h) to membranes was shown to be concentration dependent and saturable, and it was characterized by a single dissociation constant (KD = 86 ± 16 nM) with a maximal binding capacity of 54 ± 8 pmol/mg of vesicle protein. Specific binding was decreased in a concentration-dependent manner by the addition of exogenous heparin, and binding was virtually eliminated (less than 6% control values) by pretreatment of membranes with bacterial heparinase. Cultured intestinal epithelial cells (CaCo-2), shown to possess membrane-associated heparin, also bound pancreatic triglyceride lipase in a specific and saturable manner, with KD = 77 ± 12 nM and Bmax = 13.7 ± 6 pmol/106 cells. Soluble heparin not only decreased binding, but it also diminished the enzyme-mediated cellular uptake of [14C]oleate from [14C]triolein by over 75%. Therefore, intestinal heparin, a component of the brush border membrane, localizes pancreatic triglyceride lipase in a receptor-like manner to the plasma membrane to promote the subsequent absorption of fatty acids derived from hydrolyzed triglycerides.