[Determination of lipase catalytic activity with 2,3-dimercapto-1-propanol-tributyrate as substrate]

The two point test for the determination of lipase by Kurooka et al. (J. Biochem. Tokyo 81, 361-369 (1977)) was studied in detail. This procedure uses 2,3-dimercapto-1-propanol-tributyrate as substrate and Ellman's reagent as an acceptor for the released thiol groups. The time course of the enzymic hydrolysis of the substrate showed a pronounced lag phase, which can be influenced by sodium glycocholate. There is no proportionality between the quantity of added serum and the concentration of released thiol groups. Preincubation of the sample with the esterase inhibitor, phenylmethylsulphonylfluoride, as recommended by the authors, does not completely inhibit the serum esterase activity. The action of sodium dodecyl sulphate, which is included in the system, is not explained; in the continuous titrimetric test with triolein as substrate, it acts as a powerful lipase inhibitor. Using 104 serum samples, significant differences were found between the results from this method and those obtained by the titrimetric determination of lipase. Possible fundamental improvements of this test system, using thioesters as substrate, are discussed.