Intermediary metabolism is also referred to as intermediate metabolism. It involves all metabolic processes at the interface of anabolic and catabolic metabolism. Disorders of intermediate metabolic processes are usually due to enzymatic defects and manifest predominantly as storage diseases.
What is intermediate metabolism?
Intermediate metabolism is all metabolic processes at the interface of anabolic and catabolic metabolism. Figure shows metabolism at the cell wall. Metabolism (also called metabolism) is divided by medicine into anabolism and catabolism. Anabolism is used to build up chemical compounds. Catabolism serves the degradation of the same. A third metabolic reaction is amphibolism. This term is associated with intermediate metabolism. Metabolic reactions of intermediate metabolism refer to metabolites with a small molecular mass below 1000 g/mol. These metabolites are converted into each other in the reactions of intermediate metabolism. Depending on demand, intermediary metabolism obtains metabolites from catabolism or anabolism for this purpose. Unlike these two concepts of metabolism, intermediary metabolism is not associated with either specific breakdown or buildup. Amphibolism can have both catabolic and anabolic effects. Ultimately, intermediate metabolism encompasses all metabolic reactions that occur at the individual interfaces of anabolism and catabolism. Catabolism corresponds to largely oxidative degradation of large molecules (carbohydrates, lipids, proteins), and anabolism is considered to be the enzymatic synthesis of molecular cellular components.
Function and task
Catabolism breaks down large molecules of food into smaller molecules to release energy and conserve information-rich phosphate bonds as adenosine triphosphate. Catabolism has three main stages. Stage 1 corresponds to the breakdown of large nutrient molecules into individual building blocks. Polysaccharides, for example, become hexoses and pentoses. Fats become fatty acids and glycerol. Proteins are broken down to individual amino acids. Step 2 corresponds to the conversion of all molecules formed in step 1 to simpler molecules. In stage 3, the products from stage 2 are transferred to final degradation and thus oxidation. The result of this stage is carbon dioxide and water. Anabolism predominantly corresponds to a synthesis process that results in more complex and larger structures. The increase in size and complexity is accompanied by an entropic decrease. Anabolism relies on the supply of free energy, which it extracts from the phosphate bonds of ATP. Like catabolism, anabolism occurs in three stages. In the first stage, it draws on the small building blocks of catabolic stage 3. Stage 3 of catabolism is thus at the same time stage 1 of anabolism. The catabolic and anabolic metabolic pathways are thus not identical, but have the catabolic stage 3 as a connecting and central element. This stage thus represents a common metabolic step. The common central pathway of catabolism and anabolism is amphibolism. This central pathway has dual functions and can both catabolically result in the complete degradation of molecules and anabolically provide smaller molecules as starting materials for synthesis processes. Catabolism and anabolism thus have interdependent processes as their basis. The first of these processes is considered to be the successive enzymatic reactions that lead to the breakdown and degradation of biomolecules. The chemical intermediate products from this process are called metabolites. The processing of substances into metabolites corresponds to intermediary metabolism. The second process characterizes each individual reaction of intermediary metabolism and corresponds to an energy exchange. This is an energy coupling. Thus, in certain pores of the catabolic reaction sequence, chemical energy is conserved by being converted to energy-rich phosphate bonds. Certain reactions of the anabolic metabolic sequence eventually draw on this energy.
Diseases and disorders
Overall metabolism provides a variety of starting points for certain diseases. Disorders of intermediary metabolism can have fatal, even life-threatening consequences.This is the case, for example, when toxic metabolites are deposited in vital organs in the course of intermediate metabolism, thus impairing the function of these organs. Mutations that lead to a deficiency or malfunction of certain metabolic enzymes are often associated with such disorders of intermediate metabolism. An imbalance between the supply and demand with respect to certain chemical substances can also result in disorders of intermediary metabolism. Mutation-related intermediate metabolism disorders include glycogen storage diseases. This group of disorders results in glycogen storage in various body tissues. Conversion to glucose is hardly possible, if at all, for the patients of these diseases. The cause is a mutation-related defect of enzymes for glycogen degradation. Glycogen storage diseases due to enzyme defects include, for example, von Gierke’s disease, Pompe’s disease, Cori’s disease, Andersen’s disease and McArdle’s disease. In addition, Hers disease and Tarui disease also fall into this disease group. The defects can affect various metabolic enzymes, for example, alpha-1,4-glucan-6-glycosyltransferase, alpha-glucan phosphorylase or alpha-glucan phosphorylase and phosphofructokinase in addition to glucose-6-phosphatase, alpha-1,4-glucosidase and amylo-1,6-glucosidase. Storage diseases due to intermediary metabolic disorders need not be glycogenoses, but may equally correspond to mucopolysaccharidoses, lipidoses, sphingolipidoses, hemochromatoses, or amyloidoses. In lipidoses, lipids accumulate in cells. In the context of amyloidoses, deposition of insoluble protein fibrils occurs intracellularly and extracellularly. Hemochromatosis is characterized by abnormal deposition of iron, and sphingolipidoses underlie lysosomal enzyme defects that cause accumulation of sphingolipids. The effect of storage disease depends primarily on the substance stored and the tissue storing it.
