Esterase

Esterase in a narrow sense also refers to a lipase that hydrolyzes lower fatty acid esters. Furthermore, proteases also have an esterase effect when they catalyze the ester hydrolysis reaction of amino acids and the like. Depending on the reaction conditions, the reaction can also be reversed, but physiologically it proceeds in the direction of decomposition. In addition, there are also group transfer reactions that are not easily distinguished from transfe-rase. With the participation of water molecules, esterase can cleave esters into acids and alcohols through hydrolysis. These enzymes are involved in various biochemical reactions, depending on their exclusive substrate, protein structure, and function.

Acetylcholinesterase

Acetylcholinesterase is a key enzyme in biological nerve conduction. Between cholinergic synapses, this enzyme can degrade acetylcholine, stop the excitatory effect of neurotransmitters on the postsynaptic membrane, and ensure that neural signals Normal transmission in organisms. With carboxypeptidase and aminopeptidase activity. Acetylcholinesterase is involved in cell development and maturation, and can promote neuronal development and nerve regeneration. Acetylcholinesterase has high activity and is necessary for the selective hydrolysis of Ach. It can hydrolyze acetylcholine (ACh) to choline and acetic acid. The type I (ie true choli-neesterase) substrate in cholinesterase has high substrate specificity because it only decomposes a narrow range of substrates centered on acetylcholine.

Figure 1. Protein structure of acetylcholinesterase.

Phosphatase

Phosphatase is an enzyme that can dephosphorylate the corresponding substrate, that is, the phosphate group on the substrate molecule is removed by hydrolysis of the phosphate monoester, and phosphate ions and free hydroxyl groups are generated. The role of phosphatase is opposite to that of kinase, which is a phosphorylase that can use energy molecules, such as ATP, to add phosphate groups to the corresponding substrate molecules. A phosphatase commonly found in many organisms is alkaline phosphatase.

Figure 2. Protein phosphatase.

Alkaline phosphatase

Alkaline phosphatase is a non-specific phosphomonoesterase that can catalyze the hydrolysis of almost all phosphate monoesters to produce inorganic phosphoric acid and corresponding alcohols, phenols, sugars, etc., and can also catalyze the transfer reaction of phosphate groups AP is also a phosphite-dependent hydrogenase. AP exists in almost all organisms except higher plants and can directly participate in phosphorus metabolism, which plays an important role in the digestion, absorption, secretion and ossification of calcium and phosphorus.

Figure 3. Alkaline phosphatase.

Phosphodiesterases

Phosphodiesterases (PDEs) have the function of hydrolyzing intracellular second messengers (cAMP, adenosine cyclic phosphate or cGMP, guanosine cyclic phosphate), degrading intracellular cAMP or cGMP, thereby ending the biochemical effects of these second messengers. cAMP and cGMP play an important role in regulating cell activity. The regulation of its concentration is mainly determined by the balance between the synthesis of adenylate cyclase and the hydrolysis of phosphodiesterases. PDEs are widely distributed in the human body, and their physiological roles involve multiple research fields. In recent years, as a new therapeutic target, PDEs have attracted extensive attention from many scholars and become a new research hotspot. The clinical research of selective PDE 4 and PDE 5 inhibitors has received special attention. As the second messengers of neurotransmitters, hormones, light and odor, cAMP and cGMP are widely used in target organs such as kinases, ion channels and various PDEs. When foreign signals are transmitted across the membrane and cause a series of physiological reactions to activate the nucleotide cyclase, cAMP and cGMP are produced, and the mission of the PDEs family is to inactivate it by hydrolysis to 5-phosphate mononucleoside (monophosphate nucleoside 5, AMP). The balance between the synthesis of nucleotide cyclase and the hydrolytic inactivation of PDEs determines the concentration of the second messenger cAMP and cGMP. It is worth noting that cGMP is not only hydrolyzed by PDEs, but also can regulate the activity of some PDEs. For example, PDE2 can be stimulated by cGMP, while PDE3 can be inhibited by cGMP, and PDE4 is not sensitive to cGMP.

Figure 4. Phosphodiesterases.

Exonuclease

Exonuclease cuts working nucleotides one at a time from the end (outside) of a polynucleotide chain. A hydrolysis reaction occurs, breaking the phosphodiester bond at either the 3 'or 5' end. Its close relative is an endonuclease, which cleaves phosphodiester bonds in the middle (endo) of the polynucleotide chain. Eukaryotes and prokaryotes have three types of exonucleases involved in the normal conversion of mRNA: 5 'to 3' exonuclease (Xrn1), which is a dependent shell protein; 3 'to 5' exonuclease Dicer, an independent protein; and poly (A) specific 3 'to 5' exonuclease.

Reference