Lipases belong to a class of enzyme that can catalyze the heterogeneous reactions involving insoluble substrates. Lipases hydrolyze ester bonds in lipids and solubilize them into other products. Lipase plays an important role in lipid metabolism and therefore it is one of the very important enzymes in nature. Due to the heterogeneous characteristic of the enzymatic reactions involving lipase, it is difficult to accurately measure its activity in a system containing insoluble substrates. One way of measuring its activity is by the turbidimetric method.

Synthetic polyester urethane (PUR) is a water insoluble solid polymer that contains ester bonds in its polymer backbone. Hydrolysis of PUR by using esterase enzymes has been well documented in the literature. Therefore, solid PUR particles can provide a unique opportunity to measure the activity of lipases/esterases in a heterogeneous system.

In this research, the activity of Candida rugosa lipase (type VII, 59 kDa) was measured by using solid PUR particles in aqueous suspensions. Commercially available aqueous suspension of PUR particles (trade name Impranil DLN) by Bayer USA was used as a substrate. Impranil DLN is a milky white, opaque, 40% (w/w) aqueous suspension of PUR with average particle diameter of 0.2 micro meter and specific gravity of 1.0485. The decrease in optical density of the PUR suspension at 600 nm was monitored by using UV-Visible spectrophotometer under various temperature, pH, enzyme and substrate concentrations. This research shows that aqueous suspensions of PUR particles can be used to estimate the activity of lipase by turbidimetric method.

Key words: Turbidimetry, activity assay, Candida rugosa, lipase, polyester urethane, hydrolysis