What is phospholipase?
Phospholipase is an enzyme that splits fatty acids from phospholipids. The more precise classification is made into four main groups. Besides phospholipids, other lipophilic (fat-loving) substances can be split by the enzyme.
The enzyme belongs to the group of hydrolases. This means that one molecule of water is consumed during the process of cleavage and is incorporated into the two resulting products. The enzymes can have many different consequences. Depending on their localization and type, various signaling pathways or reactions can be initiated.
What types are there?
The enzyme phospholipase occurs in several forms within the body. Phospholipases are divided into four main groups: Furthermore, phospholipase A can be divided into a phospholipase A1 and a phospholipase A2. The division is based on the localization where the separation between phospholipid and fatty acid occurs.
Phospholipase C and phospholipase D actually belong to the group of phosphodiesterases.
- Phospholipase A
- Phospholipase B
- Phospholipase C
- Phospholipase D
Phospholipase A has different tasks depending on its localization and type. While phospholipase A1 plays a subordinate role in humans, phospholipase A2 is much more common.
This enzyme cleaves the bond between fatty acids and the second carbon atom of glycerophospholipids. In contrast, phospholipase A1 cleaves the bond between fatty acids and the first carbon atom of glycerophospholipids. In humans, the unit of fatty acids and glycerophospholipid is found not only in food but also in the cell walls of all cells in the body.
The splitting of the bond is on the one hand essential for the degradation of the substances. In order to ensure the adequate absorption of substances into the body during digestion, phospholipase A2 is found, among other things, in the digestive secretion of the pancreas. Via the excretory ducts of the pancreas, this secretion reaches the small intestine, where the enzyme splits fats into smaller components.
The components can then be absorbed through the mucous membrane. On the other hand, the split fatty acid serves as the starting substance for the synthesis of tissue hormones, so-called prostaglandins, which take over a variety of tasks in the body. Phospholipase A2 thus serves, among other things, to regulate inflammation and the body’s temperature regulation.
Certain drugs such as painkillers (ASA) or glucocorticoids can inhibit the enzyme and be used for therapeutic purposes. Phospholipase B also cleaves fatty acids from glycerophospholipids. In contrast to the phospholipases A1 and A2, however, this can not only take place at one of the carbon atoms of the glycerophospholipid, but at the first and second carbon atom.
Thus phospholipase B combines the properties of both phospholipases of main group A. For this reason, it also has the same tasks. In order to make a sufficient absorption of substances into the body even more effective during digestion, phospholipase B is also found in the digestive secretion of the pancreas.
In the intestine, the enzyme splits fats into smaller components. This enables them to be absorbed. In addition, after splitting off, the enzyme also provides a fatty acid as a starting substance for the synthesis of prostaglandins.
Thus, phospholipase B also serves to regulate inflammation and temperature regulation of the body. This can also be inhibited by various drugs. There are several sub-forms of this enzyme, but they do not differ in their effect.
The difference lies rather in the type of receptor-mediated increase in its activity. In comparison to the phospholipases A and B, phospholipase C differs in the place where it cleaves a bond. While phospholipases A and B cleave a fatty acid from the glycerophospholipid, phospholipase C cleaves the bond between glycerol and the phosphate group at the third carbon atom.
This releases a polar molecule which, due to its charge, can move freely in the cytosol of the cell. This is an essential part of the enzyme’s task. The substrate that is converted by the enzyme is called phosphatidylinositol-4,5-bisphosphate.This is also a glycerophospholipid with a polar, charged and an apolar, uncharged portion.
For this reason, the molecule is able to sit in the plasma membrane of a body cell. As soon as a special stimulus receptor-mediated outside the cell increases the activity of phospholipase C, the substrate is converted. The resulting polar inositol triphosphate (IP3) and apolar diacylglycerol (DAG) serves the cell as a “second messenger” in the context of stimulus transmission within the cell.
The phospholipase D is widely distributed. Like phospholipase C, it belongs to the group of phosphodiesterases. It can be further divided into the two isoforms phospholipase D1 and phospholipase D2.
Depending on the isoform, they occur with varying frequency in the compartments and organelles of the cell. Depending on their localization they take over different tasks. The substrate of the enzyme is the so-called phosphatidylcholine or lecithin.
This is a component of all cell membranes and contributes with its polar and apolar parts a large part to the function of the cell membrane. In humans, phospholipase D also plays an important role in many processes within the cells. Among other things, it is responsible for signal transduction, the movement of the cells or the organization of the cytoskeleton.
These effects are mediated by the cleavage of phosphatidylcholine to its components choline and phosphatidic acid. Phospholipase D is regulated in many ways. For example, hormones, neurotransmitters or fats can influence the activity.
Phospholipase plays a role in some diseases. However, it is not always clear what exactly this role is. In some neurodegenerative diseases such as Alzheimer’s disease, phospholipase D is discussed to be involved.