On the binding of bile salt to pancreatic lipase

The binding of taurodeoxycholate to pancreatic lipase and a few other proteins has been studied with equilibrium dialysis and in gel filtration experiments. A three compartment dialysis cell has been used; with this cell, complete equilibration is not necessary for calculation of the binding even at bile salt concentrations above the critical micellar concentration. The results indicate that taurodeoxycholate does not bind to lipase below the critical micellar concentration, that the binding starts in the critical micellar concentration range of the bile salt and reaches around 12 mol taurodeoxycholate per mol of lipase at taurodeoxycholate concentrations well above the critical micellar concentration. Previous results indicating a binding of maximally 1-2 mol taurodeoxycholate/mol lipase were too low, depending on the experimental conditions in which complete equilibration was not obtained. The binding isotherm for taurodeoxycholate to lipase is similar to that for co-lipase; colipase and lipase in mixture bind as much taurodeoxycholate as the sum for the single proteins. Taurodeoxycholate binds to ribonuclease and chymotrypsinogen to a similar extent as to lipase.