The phospholipases they are enzymes that catalyze the hydrolysis of phospholipids. These are the most abundant and important lipids in the membranes of all cellular organisms and have both structural and metabolic and signaling functions. Phospholipids are chemical molecules of an amphipathic nature, that is, they have a hydrophilic polar end and a hydrophobic apolar end..
The polar end is formed by the molecules associated with the phosphate group of a molecule of diacyl glycerol 3-phosphate. The apolar end is made up of the two aliphatic chains that are esterified to the glycerol molecule through the carbons at the C-1 and C-2 positions..
Phospholipases act by hydrolyzing any of the four ester bonds that join aliphatic chains, the phosphate group or the "head" groups that identify each type of phospholipid..
The products of its enzymatic action correspond to lysophospholipids, diacylglycerols or phosphatidic acids, which can also be substrates for other phospholipase or lipase enzymes in general..
They exist in most cells as secreted proteins, transmembrane proteins or as intracellular enzymes with multiple and varied functions, among which their participation in signaling cascades stands out..
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Some phospholipases, such as phospholipases A, are among the smallest enzymes described, with weights between 13 and 15 kDa, while others, such as phospholipases C and D, exceed 100 kDa.
Depending on the type of phospholipase considered, these can be soluble proteins or integral membrane proteins, which greatly conditions the characteristics of their amino acid sequences and their structural arrangements..
Some of these enzymes have specific sites in their structure for the binding of divalent cations such as calcium, which appear to have important functions in their catalytic activity..
Many of these enzymes are synthesized as zymogens (inactive precursors) that require the proteolytic action of other enzymes for their activation. Its activity is regulated by many cellular factors.
The most prominent function of phospholipase enzymes is that of the degradation of membrane phospholipids, either for purely structural, metabolic or intracellular communication purposes..
In addition to these degradation functions, these enzymes may have important actions in certain biosynthetic processes, since they perform “remodeling” tasks when they act in synergy with other acyltransferase proteins to alter the fatty acid skeleton of the different phospholipids..
Among the phospholipase-dependent biosynthetic processes that have been described are the production of arachidonic acid, and the biosynthesis of prostaglandins, prostacyclins, thromboxanes and others..
Phospholipase C participates in the hydrolysis of phosphatidylinositols, releasing molecules derived from these that have important functions as second messengers in numerous intracellular communication and signaling processes..
There are two main sets of phospholipases: acylhydrolases and phosphodiesterases. The classification within each set is based on the position of the hydrolytic cut that they perform on the different ester bonds that unite the “pieces” of the phospholipids on which they act..
They are not strictly specific regarding the type of phospholipid (according to the identity of the polar group or its hydrocarbon chains) but rather regarding the position of the bonds in the backbone of glycerol 3-phosphate or 1,2-diacyl glycerol 3- phosphate.
Phospholipases A and B belong to the group of acylhydrolases, while phospholipases C and D belong to phosphodiesterases..
This group of phospholipases is responsible for the hydrolysis of the acyl-esters that are attached to the carbons in the C-1 and C-2 positions of the diacylglycerol molecule..
Phospholipases A1 are known as those that hydrolyze the ester bonds between the aliphatic chain and carbon 1 and A2 that hydrolyze the ester bonds between the aliphatic chain and carbon 2 of glycerol.
Phospholipases A1 are generally intracellular proteins, large in size and generally associated with the plasma membrane. Phospholipases A2, on the other hand, are stable extracellular proteins, of very small size and soluble in water..
The first phospholipases described were type A2, which were obtained from pancreatic juices of mammals and the venom of cobra snakes..
The enzymes belonging to this group can hydrolyze the ester bonds between any of the two fatty acid chains of a phospholipid (at the C-1 and C-2 positions) and can also act on lysophospholipids..
They have been found in many species of microbes, protozoa and mammalian cells and are part of the virulence factors of many pathogenic fungi.
The enzymes belonging to this group are responsible for the hydrolysis of the phosphodiester bonds between the glycerol molecule and the phosphate group (Phospholipase C) producing 1,2-diacylglycerols, and between the phosphate group and the polar group attached to it (Phospholipase D ), producing phosphatidic acids.
Phospholipase C was first purified from the culture medium of many types of bacteria, but it is found in a wide variety of mammalian cells.
Most of these enzymes act preferentially on phosphatidylcholine, but show activity against other phospholipids such as phosphatidylinositol.
Phospholipase D has been widely studied in plant tissues such as cabbage, cotton and corn seeds, etc. However, it has also been detected in mammals and some microorganisms. They are large enzymes, usually more than 100 kDa in molecular weight.
These are the enzymes responsible for the hydrolysis of fatty acids linked to lysophospholipids (phospholipids on which a phospholipase A has acted, for example, and which have a single fatty acid chain attached).
They are known as Phospholipases L1 and Phospholipases L2 depending on the carbon atom of the glycerol molecule on which they act..
These enzymes have been purified from many microorganisms, the venom of some insects, eosinophilic cells, and many different mammalian tissues..
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