Lipase

Lipase is an enzyme i.e. a biological catalyst that catalyzes the hydrolysis of the fats or lipids. These enzymes are subclasses of the esterases. The main lipase enzyme function is to digest the heavy fat molecules during digestion. They are responsible for the transport and the processing of the dietary lipids like the triglycerides, fats, oils, etc. in most of the living organisms. The genes encoding the lipase enzyme are also present in some of the viruses. Thus, the lipase enzyme is a fat-splitting enzyme that is commonly present in the blood. 

Structure and Catalytic Mechanism of Lipase Enzyme

There are several genes present in nature that are known to express lipases and which determine how lipase work and what kind of structure the enzyme should adapt to carry out the required lipase function. There are very distinct arrays of genes that control the various protein folds of the enzyme, not only making it’s structure suitable for specific purposes but also determining what will be the catalytic mechanism which defines the role of lipase at a particular site. For example, there are several enzymes such as the human pancreatic lipase, phospholipases, sphingolipides, that carry out the activity of hydrolysing the fats or lipids but under different conditions and different organs of different living organisms. 

The usual site of the lipase activity is the glycerol backbone of a lipid substrate. An example of this is the human pancreatic lipase (HPL) that is released by the pancreas and is the main enzyme that is known for catalyzing the reaction to break down the dietary fats in the human digestive system. The main purpose of the HPL lipase is the conversion of triglycerides substrates, which is a very common oil ingredient in the food we eat, into the monoglycerides and fatty acids. Hence, in this case, the lipase enzyme function is to help the body in digesting the triglycerides which are heavy fat substrates into the basic components which are the monoglycerides and fatty acids. 

Most of the lipase function is determined by their structure. As many of the commonly found lipases or the conventional lipases are fat-digesting enzymes, they share a common protein fold. Most of these enzymes contain an alpha/beta hydrolase fold. The lipase enzyme function employs a chymotrypsin-like mechanism that uses a catalytic triad (i.e. a set of three coordinated sites forming the active site of the enzyme) consisting of a serine which is a nucleophile, a histidine base, and an acid residue which in most cases is an aspartic acid. An example of such a structure is given below:

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Where is Lipase Produced?

There are a diverse range of biological processes that employ the lipase enzyme function. They range from routine works such as metabolism in which the lipase digests the triglycerides to the functions that are a part of the cell signaling and inflammation processes. Some of the locations of the lipase release and the corresponding functions are given below:

• Lysosomal Lipase: It is found in the lysosomes and the enzyme is confined within the organelle. 

• Pancreatic Lipase: These are secreted by the pancreas into the extracellular spaces where they perform the main function of processing the dietary fats and lipids into simple forms that are easily absorbed and then are transported throughout the body.

• Fungi and bacteria also secrete the enzymes that help in facilitating the nutrient absorption from any external source. In some cases, the pathogenic microbes secrete the lipases for invasion of a new host. 

• Certain lipases like the phospholipases are also found in the venoms of organisms such as the wasp and the bee venoms. This enhances the effectiveness of the injury and the inflammation caused by the sting.

• In cell biology, an important role is played by the lipases as they perform integral functions along with the phospholipids that comprise most of the biological membranes.

• A fungus, Malassezia globosa, which is responsible for causing the human dandruff, also utilises lipases for breaking down the sebum into oleic acid and increasing the skin cell production thus resulting in dandruff. 

Common Lipases Found in Humans

One of the most common lipases found in human beings is the pancreatic lipases released by the pancreas that play a vital role in the human digestive system. Another one of such lipases is pancreatic lipase related protein 2 (PLRP2). Other common examples are given below:

• Hepatic Lipase: This enzyme is introduced in the endothelium. This lipase digests the remaining lipids that are carried on by the lipoproteins in the blood for regenerating low density lipoprotein. 

• Lipoprotein Lipase: This is another lipase found in the endothelium. This lipase digests the triacylglycerides carried on by the very low density lipoprotein. After this, the fatty acids that are freed are again taken up by the cells. 

• Gastric Lipase: It is one of the lipases commonly present in the digestive juices. This lipase functions in the body at a near-neutral pH for the digestion of the lipids. 

• Bile-Salt Dependent Lipase: This lipase breaks down the fats in the digestive system and is produced by the pancreas and the breast milk. 

 Use of Lipases

There are many uses of lipases not only in biological processes but also in industrial and diagnostic purposes. Some of the lipases are expressed and secreted by pathogenic organisms for their protection and invasion purposes during an infection. In blood tests, the lipases are used for identifying and diagnosing acute pancreatitis and other such disorders that are related to the pancreas. In industrial usage they are widely used in the milk products industry. They have been used since ancient times in human practices for yogurt and cheese fermentation. They are also used as biocatalysts for baking, laundry detergents and other products that deal with household applications. 

Lipases showing high enzyme activity that can be used for the processing of biodiesel. This is because the lipases are environmentally friendly and are safe. Other industrial applications involve the use of lipases in process intensification especially for continuous processing like the continuous flow microreactors at a small scale. Thus, these are vital enzymes not only for biological applications but also for various industrial applications as well.