Lipase is an enzyme found in active form in the serum of man and many animals. Lipase is primarily a digestive enzyme that hydrolyzes triglycerides into fatty acids. In dogs, serum lipase activity is used to diagnose and monitor acute pancreatitis.
Many veterinary laboratories use a complex multistep colorimetric reaction to detect lipase using 1,2-diglyceride as the substrate. In this reaction scheme lipase catalyzes the hydrolysis of 1,2-diglyceride to yield a monoglyceride and a fatty acid. With the participation of several additional enzymes the monoglyceride is altered to glycerol, glycerol is reduced generating a peroxide and a quinone dye is the eventually result of the end point reaction.
A new, liquid stable colorimetric assay for determining lipase activity in serum has been introduced. (1) This test requires only one enzyme, lipase, to catalyze the hydrolysis of the novel substrate 1,2-o-dilauryl-rac-glycero-3-glutaric acid-(6' methylresorufin) ester (DGGR).
Using canine serum, the DGGR substrate assay was compared to the 1,2-diglyceride substrate assay. There was an increased specificity of canine lipase for the DGGR substrate. The Km (Michaelis constant) was 6.4 times smaller for the DGGR substrate than the 1,2-diglyceride substrate while the kcat and the Vmax values were 2.7 times greater for the DGGR substrate.
Other comparative studies between these two substrates have shown major differences in the expected normal range values for different species. The normal range ratio of the 1,2-diglyceride substrate to the DGGR substrate is 5.3:1 for dogs, 4.1:1 for cats and 1.6:1 for humans. A potential explanation for this difference between normal range values may be a non-lipase specific interaction with the multi-enzyme cyclic reaction mechanism of the 1,2-diglyceride substrate complex. This is most noticeable when using canine serum.
The DGGR assay, therefor, offers increased specificity, faster reaction rates and liquid stability.

Joel Glovsky, Ph.D.
NuClin Diagnostics, Inc.
Northbrook, Illinois

Reference:
1) Panteghini M, Bonora R and Pagani, F. Measurement of pancreatic lipase activity in serum by a kinetic colorimetric assay using a new chromogenic substrate. Ann Clin Biochem 2001; 38: 365-370.