INTERACTIONS BETWEEN PANCREATIC LIPASE, CO-LIPASE, AND TAURODEOXYCHOLATE IN ABSENCE OF TRIGLYCERIDE SUBSTRATE

The interactions between lipase [EC 3.1.1.3], by calorimetry and circular dichroic determinations. Porcine pancreatic lipase binds to co-lipase to form a 1:1 complex with an association constant of 2 .times. 106 M-1. The binding is exothermic and proceeds with an increase of entropy and the .DELTA.Cp [specific heat at constant pressure] of the reaction is highly negative, -1.31 kJ.degree. K-1 (mol of lipase)-1 at 25.degree. C. This is interpreted to be due to hydrophobic interactions between lipase and co-lipase. The binding of taurodeoxycholate to lipase and co-lipase is an endothermic process, which proceeds without any gross conformational changes as judged by circular dichroisc measurements, although spectral changes are observed in the aromatic region. No binding between taurodeoxycholate and co-lipase is detected until concentrations near the critical micellar concentration of the former are reached. Taurodeoxycholate and co-lipase may form mixed micelles.