Pancreatic lipase and co-lipase. Interactions and effects of bile salts and other detergents.

Abstract

The effect of conjugated bile salts on the activity of pancreatic lipase depends on their concentration in relation to their critical micellar concentration.Below the critical micellar concentration, conjugated bile salts slightly stimulate the initial rate of hydrolysis of tributyrine, an effect that may be caused by a protection of the enzyme from inactivation at the substrate‐water interface.Above the critical micellar concentration, conjugated bile salts almost completely inhibit lipase. The inhibition is more marked in alkaline reactions resulting in a pH optimum shift with increasing bile salt concentration. Bile salt inhibition of lipase is related both to the concentration of bile salt and to the substrate concentration or rather to substrate surface area, and most probably is complete when the interface is saturated with detergent.Co‐lipase, in the absence of bile salts, stimulates the activity of lipase, 1.3 to 1.4‐fold in the whole pH range of its activity. Co‐lipase overcomes the inhibition of lipase caused by bile salts with a shift in the pH optimum to 6–7 compared to 8–9 for lipase alone.The different conjugated bile salts have similar effects, consideration being taken to differences in their critical micellar concentration; free bile salts have a less inhibitory effect on lipase and the stimulation by co‐lipase shows no pH optimum shift.Detergents of the acyltaurine type such as decanoyltaurine and dodecanoylsarcosyltaurine inhibit lipase in a similar manner to the conjugated bile salts and this inhibition is also released by co‐lipase. Detergents such as dodecylsulphate above the micellar concentration, irreversibly inhibit lipase. The simultaneous presence of bile salts protects the enzyme from being irreversibly inactivated.Lipase and co‐lipase interact in a stoichiometrical relationship and it appears justified to classify co‐lipase as a co‐enzyme for lipase.