Effects of colipase and taurodeoxycholate on the catalytic and physical properties of pancreatic lipase B at an oil water interface.

W E Momsen,H L Brockman

doi:10.1016/s0021-9258(17)33889-9

Abstract

A monolayer reaction system employing tripropionin and siliconized glass beads was used to study the effects of taurodeoxycholate and colipase on the catalytic activity, interfacial stability, and interfacial affinity of porcine pancreatic lipase B (EC 3.1.1.3) The stability and catalytic activity of lipase at the bead-water interface are governed by the same two ionizable groups with pKa values (in the absence of cofactors) of 5.6 and 9.3. Colipase alone or with bile salt caused only a slight perturbation of these values. At low concentrations, 0 to 0.3mM, taurodeoxycholate increases the stability of lipase by 5-fold. At higher concentrations, 0.3 to 0.8 mM, but still below its critical micelle concentration, taurodeoxycholate prevents the adsorption of lipase to the bead-water interface. This appears to be the major mechanism by which this bile salt inhibits lipolysis. Colipase exerts small positive effects on lipase stability and catalytic activity. More importantly, colipase enables the adsorption of lipase in the presence of bile salt, thereby reversing the inhibition.

Highlights

At low concentrations, 0 to 0.3 mM, taurodeoxycholate increases the stability of lipase by &fold
It causes a stimulation of the rate of hydrolysis in the absence or presence of bile salts and it markedly improves the linearity of product formation as a function of time [5]
With such a system we have examined the effects of sodium taurodeoxycholate and pancreatic colipase on the hydrolysis of the partially soluble triglyceride, tripropionin, by pancreatic lipase B adsorbed to hydrophobic, siliconized glass beads

Summary

Introduction

0 to 0.3 mM, taurodeoxycholate increases the stability of lipase by &fold. By employing monolayers of substrate, or enzyme, or both, of a known composition and area, it has been possible to measure kinetic and thermodynamic parameters both accurately and reproducibly (l-4) The results of such studies with pancreatic lipase have indicated that in a well defined, monolayer system the metal ions, bile salts, albumin, and other cofactors used in emulsion assays are unnecessary for catalytic activity [1]. The recent development of well defined, monolayer reaction systems eliminates many of the difficulties encountered in working with emulsions With such a system we have examined the effects of sodium taurodeoxycholate and pancreatic colipase on the hydrolysis of the partially soluble triglyceride, tripropionin, by pancreatic lipase B adsorbed to hydrophobic, siliconized glass beads. This system [3] was chosen in preference to other monolayer methods because the measurements obtained are not directly sensitive to surface tension changes induced by bile salts

Methods

Results

Conclusion