Inhibition of lipases by proteins. A kinetic study with dicaprin monolayers.

The research investigates how proteins inhibit the function of certain lipases, which are enzymes that break down fats. The study focused on pancreatic and microbial lipases, using monolayers of dicaprin, a fat molecule, to observe inhibition patterns and understand the variables that affect interactions between lipases and proteins.

Studying Protein Inhibition of Lipases

• The study used a monolayer technique to closely examine the inhibition of pancreatic and microbial lipases by various proteins, including beta-lactoglobulin A, melittin, serum albumin, and myoglobin, as well as a protein that inhibits lipase derived from soybeans.
• The research revealed that when these proteins were pre-incubated with a dicaprin film under certain conditions, there was no lipase activity detected from horse pancreatic lipase or Rhizopus delemar lipase.
• However, the lipase activities of Rhizopus arrhizus and Geotrichum candidum were not impaired under similar conditions, highlighting different reactions to protein inhibitors among different types of lipases.

Understanding the Mechanism of Lipase Inhibition

• The researchers performed experiments using mixed lipid-protein film transfers to clarify the inhibition mechanism. The results confirmed that the inhibition of the pancreatic lipase occurs due to the protein’s association with lipids, and not from direct interactions between the protein and enzyme in an aqueous phase.
• This finding implies that the protein’s inhibition capacity is highly dependent on its interaction with the lipid, rather than its potential for direct interaction with the enzyme itself.

Finding Correlations in Inhibition Ability and Surface Properties

• The study also endeavored to link the surface properties of the proteins to their inhibition capacities. They used three parameters – the initial rate of surface pressure increase, the maximal surface pressure increase, and the critical surface pressure – to evaluate these properties at the interface between dicaprin (a diglyceride) and water.
• They found a positive correlation between the initial rate of surface pressure increase of the proteins and their respective ability to inhibit pancreatic and R. delemar lipases. No correlation, however, was observed with the other two parameters, demonstrating the importance of the initial rate of surface pressure increases in relation to inhibition capacity.