THE AFFINITIES OF PROCOLIPASE AND COLIPASE FOR INTERFACES ARE REGULATED BY LIPIDS

It has been suggested that at physiological pH, the trypsin-catalyzed activation of the lipase cofactor, procolipase, to colipase has no con sequence for intestinal lipolysis and serves primarily to release the N-terminal pentapeptide, enterostatin, a satiety factor (Larsson, A., and C. Erlanson-Albertsson. 1991. The effect of pancreatic procolipase and colipase on pancreatic lipase activation. Biochim. Biophys. Acta 1083:283-288). This hypothesis was tested by measuring the adsorption of [C-14]colipase to monolayers of 1-stearoyl-2-oleoyl-sn-3-glyceropho sphocholine and 13,16-cis, cis-docosadienoic acid in the presence and absence of procolipase. With saturating [C-14]colipase in the subphase , the surface excess of [C-14]colipase is 29% higher than that of proc olipase, indicating that colipase packs more tightly in the interface. With [C-14]colipase-procolipase mixtures, the proteins compete equall y for occupancy of the argon-buffer interface. However, if a monolayer of either or both lipids is present, [C-14]colipase dominates the ads orption process, even if bile salt is present in the subphase. If [C-1 4]colipase and procolipase are premixed for >12 h at pH similar to 8, this dominance is partial. If they are not premixed, procolipase is es sentially excluded from the interface, even if procolipase is added be fore [C-14]colipase. These results suggest that the tryptic cleavage o f the N-terminal pentapeptide of procolipase may be of physiological c onsequence in the intestine.