Where Is Lipase Found and How Does It Work?
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.
FAQs on Lipase: Structure, Functions, and Significance
1. What is the lipase enzyme and what is its primary function in the human body?
Lipase is a water-soluble enzyme that plays a crucial role in digestion. Its primary function is to catalyse the hydrolysis, or breakdown, of fats (lipids), specifically triglycerides, into smaller, more easily absorbable molecules: fatty acids and glycerol. This process is essential for the body to absorb and utilise dietary fats for energy, cell structure, and other vital functions.
2. Where is lipase produced in the body and where does it primarily act?
Lipase is produced in several locations, but the main sources are:
- Pancreas: The pancreas produces pancreatic lipase, which is the most significant lipase for fat digestion.
- Stomach: The stomach secretes gastric lipase, which begins the process of fat digestion.
- Mouth: Salivary glands in the mouth produce lingual lipase.
While digestion begins in the mouth and stomach, the primary site of action for lipase, particularly pancreatic lipase, is the small intestine (specifically the duodenum), where most fat digestion and absorption occur.
3. What are the end products when lipase breaks down fats?
When lipase acts on its substrate, which are triglyceride fats, it breaks them down into simpler components that can be absorbed by the intestinal lining. The primary end products of this enzymatic reaction are three fatty acid molecules and one glycerol molecule. These products are then absorbed and reassembled or used for energy by the body.
4. How does the pH of the digestive tract affect the function of different lipases?
The activity of enzymes like lipase is highly dependent on pH. Different lipases are optimised to work in different environments:
- Gastric Lipase: Secreted in the stomach, it functions optimally in the highly acidic environment (pH 3-6) of the stomach.
- Pancreatic Lipase: This enzyme functions in the small intestine, which is neutralised by bicarbonate from the pancreas. Therefore, it works best in a slightly alkaline environment (pH 8.0).
5. What is the clinical significance of measuring lipase levels in the blood?
Measuring lipase levels in a blood test is a crucial diagnostic tool, primarily for assessing the health of the pancreas. Normally, blood lipase levels are very low. However, if the pancreas is inflamed or damaged, as in conditions like acute pancreatitis, it releases large amounts of lipase into the bloodstream. Therefore, significantly elevated lipase levels are a key indicator of pancreatic injury or disease.
6. Why is the emulsification of fats by bile salts essential for lipase to function effectively?
Fats are hydrophobic (water-repelling) and tend to clump together into large globules in the watery environment of the intestine. Lipase is a water-soluble enzyme and can only act on the surface of these fat globules. Bile salts, produced by the liver, act as detergents to break down these large globules into thousands of tiny droplets. This process, called emulsification, dramatically increases the surface area of the fat, allowing the water-soluble lipase enzyme to access and break it down far more efficiently.
7. How does hormone-sensitive lipase (HSL) differ from digestive lipases?
Hormone-sensitive lipase (HSL) is functionally different from digestive lipases like pancreatic lipase. The key differences are:
- Location: HSL is an intracellular enzyme found inside fat cells (adipocytes), whereas digestive lipases are extracellular and work in the digestive tract.
- Function: The role of HSL is not to digest dietary fat, but to mobilise stored fat. It breaks down triglycerides stored within fat cells into fatty acids, releasing them into the bloodstream to be used for energy by other tissues.
- Regulation: HSL's activity is regulated by hormones like epinephrine and glucagon, not by the presence of food in the gut.
8. Beyond digestion, what are some important industrial applications of the lipase enzyme?
The catalytic ability of lipase is utilised in various industries. Important applications include:
- Food Industry: Lipases are used in the dairy industry for the ripening of cheese and to develop specific flavours. They are also used in baking and to improve the texture of food products.
- Detergent Manufacturing: Lipases are added to biological washing powders and detergents to help break down and remove fat-based stains like oil, grease, and lipstick.
- Biodiesel Production: Lipases are used as biocatalysts in the production of biodiesel from vegetable oils, offering an environmentally friendly alternative to chemical catalysts.
