Fluorometric Method for Measuring Serum Lipase Activity

We describe a method for determining lipase (triacylglycerol acyl-hydrolase, EC 3.1.1.3) activity in serum. Emulsified olive oil in tris(hydroxymethyl)aminomethane buffer is used as substrate. The course of the enzymatic reaction is followed by measuring the decrease in fluorescence with time of a fluorescent indicator, 4-methylumbelliferone, added to the substrate, caused by the change in the pH of the substrate solution resulting from the reaction. All measurements are performed at 37 °C. The reaction volume is about 2.3 ml, in a Pyrex cuvette. Change of fluorescence and of enzyme activity are linearly related in the range of 77.8 to 389.0 U/liter. An assay can be done in as little as 3 to 5 min, with excellent precision.

Simplified Photometric Copper-Soap Method for Rapid Assay of Serum Lipase Activity

We modified the method of Yang and Biggs [Clin. Chem. 17, 512 (1971)] for greater speed and simplicity. Serum is incubated with an emulsified olive oil substrate, the fatty acids extracted, the copper soap formed, and phases separated, all in a single tube. An aliquot of the organic phase is removed for color development. One analysis can be completed in 35 min, 20 in less than 2 h. The method is accurate and precise. Results correlate well with the unmodified colorimetric method, and with the classical titrimetric lipase procedure. The reference interval (normal range) is 20 to 180 U/liter.