[Titrimetric measurement of catalytic concentration of pancreatic lipase: state of the art].

Most lipase routine assays are carried out using either soluble substrates or emulsified substrates (triglycerides or olive oil) at low concentrations. Many of these techniques require a secondary standard, which must be titrated beforehand; the need for a reference method is thus compelling. Titrimetric assays have several advantages such as the possibility of employing high substrate concentrations allowing the direct determination of the product of lipolysis in the absence of interfering phenomena. In a recent study it was demonstrated that human lipase activity depends on the zeta-potential of the lipid droplets, the number of hydroxy groups present in each individual bile salt, the aggregation number and the conjugation of bile salts with taurine or glycine. Hydroxypropyl methylcellulose proposed by Tietz et al is to be preferred to gum arabic for being a pure, well defined emulsifier. Ultrasonic homogenizers enable volumes of oil-in-water emulsions, characterized by fine lipid droplets with good homogeneity to be obtained without overheating. Lipolytic activity is completely inhibited by 70 mmol/l of bile salt (regardless of the type) in the absence of colipase. Variable concentrations of colipase are needed to restore the lipase activity in the presence of different bile salts: optimal cofactor concentrations vary from 0.1 mg/l with deoxycholate or cholate to 6 mg/l with taurocholate or glycocholate. Even after optimization of the medium with colipase, marked differences in enzyme activity are noted depending on the bile salt used.(ABSTRACT TRUNCATED AT 250 WORDS)