Lipases, Esterases, and Phospholipases

Lipids are large, water-insoluble molecules that composed of triglycerides of fatty acids. They play important biological roles in conjunction with lipolytic enzymes. These enzymes are esterases (EC 3.1.1.1) and lipases (EC 3.1.1.3), which differ in their specificity toward the substrates. Esterases act on short chains of triglycerides (water soluble), whereas lipases act on lipids (water insoluble) (Chahinian and Sarda, 2009 Fojan et al., 2000). 

Lipases are water-soluble enzymes that naturally catalyze the hydrolysis of oils and fats, insoluble substrates, acting at the oil-water interface. Their optimum activity of lipases is reached in emulsions, where high substrate surfaces can be obtained and substrate concentrations exceed the critical micelle concentration (Meyer et al., 1990). 

The International Union of Biochemistry and Molecular Biology (lUBMB) defines lipases as glycerol-ester hydrolases and recommends that ester mulsion should be used as the substrate. The first lipase use was investigated by Claude Bernard in 1856. He studied the role of pancreas juice in fat digestion (Petersen and Drabl0s, 1994). This is a distinct feature of lipases, commonly referred to as an interface activation. Besides the interface action, lipases can also work in bulk solutions. That, however, is at lower activity levels compared to those at the interfaces (Reetz, 2002 Taipa et al., 1992 Weete et al., 2008). The kinetics of a lipase-activated reaction, therefore, are described by interfacial activation kinetics rather than the well-known Michaelis-Menten kinetics (Sarda and Desnuelle, 1958). This phenomenon is further explained in Section 2.3.3. 

In addition to hydrolysis, lipases can also catalyze transesterilication and inter-esterfications. This diversity allows lipases to be used for various applications in the field of chemical synthesis, including oil and fat splitting and modification. Details of lipase nse in various applications are provided in Section 2.6. 

Lipases differ from phospholipases. By the former, both triacylglycerols andphos-pholipidsare are hydrolyzed, whereas by the presence of the latter only phospholipids 

---

In order to carry out PHA production from triglycerides, the cells need to hydrolyze the triglycerides into free fatty acids that can be transported into the cells. For this, the cells need to secrete an enzyme called lipase. A wide variety of organisms is known to secrete lipolytic enzymes, mainly for lipid metabolism and signal transduction. Lipolytic enzymes can be classified into different classes, including lipases, esterases, and phospholipases (Arpigny and Jaeger 1999). Esterases are enzymes that hydrolyze ester bonds of soluble or partially soluble molecules. 

---