Simple proteinases and conjugated proteasesProteins are divided into simple proteins and combined proteins. Likewise, enzymes according to the chemical composition can also be divided into two main categories: simple proteinases and conjugated proteases. General hydrolytic enzymes such as urease, protease, amylase, lipase, ribonuclease, etc. are simple proteases. The activity of these enzymes depends only on their protein structure. The enzyme consists only of amino acids and does not contain any other components. And transaminase, lactate dehydrogenase (LDH), carbonic anhydrase, and other oxidoreductases are all bound proteases. In addition to protein components, these enzymes also contain small, non-protein molecules that are stable to heat. The first is called an apoenzyme, the second is called cofactors. When enzyme protein and cofactor exist alone, there is no catalytic activity. Only when the two are combined into a complete molecule can they have enzyme activity. This complete enzyme molecule is called a holoenzyme.
holoenzyme = enzyme protein + cofactor
Some enzyme cofactors are metal ions and some are small-molecule organic compounds. Sometimes they are both needed for enzyme activity. These small-molecule organic compounds are commonly referred to as coenzymes or prosthetic groups. The metal is contained in the enzyme molecule, either as a component of the enzyme's active site or to help form the conformation necessary for enzyme activity. Enzyme proteins use polar groups on their side chains to bind cofactors through covalent, coordinated, or ionic bonds by the reaction. Generally, the small molecule organics loosely bound to the enzyme protein that is readily detached from the enzyme protein and can be removed by dialysis are called coenzymes; and the small molecule substances that are tightly bound to the enzyme protein and cannot be easily removed by dialysis are called prosthetic groups. There is no essential difference between coenzymes and prosthetic groups, and there is no strict boundary between the two, except that they are strongly bound to the enzyme protein.
Enzyme proteins and cofactors play different roles in the catalytic reaction of holoenzymes. The enzyme protein determines the specificity and high efficiency of the enzyme reaction, and the cofactor acts directly as a carrier for electrons, atoms, or certain chemical groups, participates in the reaction, and promotes the entire catalytic process.
Usually, an enzyme protein can only be combined with a coenzyme to form an enzyme, which acts as a substrate to perform a one-way chemical reaction. A coenzyme can be combined with different enzyme proteins to form different enzymes, catalyzing the same type of chemical reaction from different substrates. For example, the enzyme protein of lactate dehydrogenase can only be combined with NAD to form lactate dehydrogenase, thereby becoming the substrate lactic acid dehydrogenase. But there are many types of enzyme proteins that can bind to NAD, such as lactate dehydrogenase, malate dehydrogenase (MDH), and glycerophosphate dehydrogenase (GDH) containing NAD, which can catalyze separately. Lactic acid, malic acid, and glycerol phosphate are dehydrogenated. It can also be seen that the enzyme protein determines the type of reaction substrate, i.e., the specificity of the enzyme, and the coenzyme (base) determines the reaction type of the substrate.
The monomeric enzyme, oligomers, and multi-enzyme complex system
According to the structural features of proteins, enzymes can be divided into three categories:Monomeric enzyme
Enzymes with only one polypeptide chain are called monomeric enzymes and cannot break down into smaller units. The molecular weight is 13,000 - 35,000. There are few such enzymes, and most are enzymes that promote the hydrolysis reaction of the substrate, i.e., hydrolytic enzymes, such as lysozyme, protease, and ribonuclease.
Enzymes that consist of several or more subunits is called oligomeric enzymes. The subunits in the oligomers can be the same or different. The subunits are joined by non-covalent bonds, which are easy to separate for acids, bases, high concentration salts, or other denaturants. The molecular weight of oligomers ranges from 35,000 to several million. Such as phosphorylase a, lactate dehydrogenase, etc.
Multi-enzyme composition system
The complex formed by the chimerization of different enzymes with each other is called the multi-enzyme system. The multi-enzyme complex is conducive to the continuous progression of a series of reactions in the cell to improve the catalytic efficiency of the enzyme. Computer Technology Articles, while at the same time helping the body to regulate and control the enzyme. The molecular weights of multiple enzyme complexes are all higher than several million. Such as pyruvate dehydrogenase system and fatty acid synthetase complex are multi-enzyme systems.