What is lingual lipase and what does it do? It is an enzyme secreted by the body which helps in digestion. For more on this, read on.
Why ‘Lingual’?
It’s probably because, lingual literally means lying near the tongue and that’s where lingual lipase is.
Before introducing you to what lingual lipase is and what it does, let me tell you what lipase is. Lipases are water-soluble enzymes that act as catalysts in the hydrolysis reaction of ester chemical bonds in water-insoluble lipid substrates. Lipases play a key role in digestive system function, the most common example of lipase being the human pancreatic lipase. It is the enzyme that breaks down fats and converts triglyceride substrates to free fatty acids and monoglycerides. Lipases have a vital role to play in fermentation processes as well. It’s the lipases from bacteria and fungi that aid cheese and yogurt fermentation. They are also being used as catalysts for lipid degradation. They are classified as:
- Preduodenal lipases
- Pancreatic lipases
Lingual lipase is a member of lipases, which, as you know by now, is a group of digestive enzymes. It belongs to the category of preduodenal lipases. Gastric lipase is the other member of this category.
Where is lingual lipase made? Which part of the body secretes this enzyme? Lingual lipase is secreted in the buccal cavity, specifically stated, by the Ebner’s glands located around the circumvallate on the tongue and is localized in the zymogen granules.
Lingual lipase breaks down short chain saturated fatty acids and helps in their digestion. It is one of the key components that aid the digestion of milk fat in newborns. It can penetrate into the milk fat globule, which makes this lipase vital to the digestive process of milk fat in newborn babies. It is found in premature babies in the 34th gestational week, which is evidence enough for the fact that lingual lipase is present at birth. Its activity increases with feeding. It hydrolyzes dietary triglycerides, forming diglycerides and free fatty acids.
It uses Aspartatic Acid-203, Histidine-257, and Serine-144 as catalysts to hydrolyze a triglyceride into a diglyceride and a free fatty acid. In the first step of this process, protons from serine are removed, making it a better nucleophile. The pair of valence electrons on the oxygen of the serine undergoes a nucleophilic addition, which means that a pi bond is replaced by two new covalent bonds through the addition of a nucleophile. Nucleophilic addition takes place specifically on the first or the third carbonyl of the triacylglycerol. Protons are added to the diglyceride leaving group, that is, it is protonated by Histidine-257. After another cycle of proton removal, the valence pair of electrons on the oxygen atom of water undergoes a nucleophilic addition reaction. Thus, we can say that lingual lipase breaks down triglycerides to form diglycerides and free fatty acids. The end products of this reaction are, a diglyceride and a free fatty acid, along with a small amount of monoacyglyceride that helps in the breaking down of food.
And not just in maintenance of digestive health, lingual lipase is active in the absence of bile salts and helps counter temporary bile salt deficiency. It has a low pH optimum, which makes it possible for this lipase to remain active even when pH levels are low. This condition is characteristic to patients of cystic fibrosis. Those suffering from cystic fibrosis are at the risk of getting affected by exocrine pancreatic insufficiency, which, in simple words, is the inability to digest food due to lack of digestive enzymes.
In some cases, pancreatic lipase may not be produced at all. And this is when lingual lipase comes to help. It can be of use in enzyme replacement therapy, as an effective treatment for pancreatic insufficiency. The absorption of dietary fat can be made possible in these patients, even in the absence of pancreatic lipase that their body cannot produce. Lingual lipase also leads to the formation of amphiphilic reaction products, thus making the dietary fat soluble.
Such is the function of lingual lipase in humans and this is how important its role is. That makes me think how small things and the roles they play make so much of a difference. To look at it, lingual lipase is just another enzyme; but it’s one of the so many more; all playing a key role in that very important process of digestion. We eat, work, and rest; never bother about what goes on inside our bodies. But what actually happens inside is so complex. There are so many things at work, in the chemical laboratory of our body. Something so complex seems to happen with great simplicity.
