Protein and lipid metabolisms interconnection

It is possible to use products of fatty acids catabolism to synthesize non-essential amino acids. Acetyl-CoA which is formed at fatty acids degradation reacts with oxaloacetate. This is condensation reaction. It leads to α-keto-glutaric acid formation through TCA cycle. α-ketoglutaric acid by amination or transamination goes into glutamic acid. However, the possibility of synthesis of the carbon skeleton of amino acids from fatty acids is limited. It is limited to the synthesis of glutamic acid. It needs the presence of oxaloacetate which is produced from other sources (carbohydrates and proteins).

In addition to fatty acids glycerol is in the composition of neutral fats. Glycerol is oxidized to glyceric acid and subsequently converted into pyruvic acid, and the latter is used for the synthesis of several amino acids. The possibility of lipid synthesis of the proteins proved unilateral protein diet, which does not cause disturbances in the metabolism.

Way of using proteins for lipid synthesis takes place through the formation of acetyl-CoA. Acetyl-CoA is formed from all amino acids on a particular stage of their oxidation and can be used for fatty acid synthesis. Glycerol is formed only from amino acids which are capable give pyruvate.

Carbohydrate and lipid metabolisms interconnection

Triglyceride molecule is composed of glycerol and fatty acids. Consequently, carbohydrates are synthesized from these lipids components in the organism. Glycerin can be formed from glycealdehyde phosphate or dihydroxyacetone phosphate– normal intermediate products of carbohydrate metabolism. The main source for the synthesis of fatty acids is acetyl-CoA. Acetyl-CoA is formed by oxidative decarboxylation of pyruvic acid in the tissues, and pyruvic acid is a normal product of carbohydrate metabolism.

The question of the possibility of lipids transformation into carbohydrates is more complicated. If in respect of glycerol such conversion is well known (phosphorylation of glycerol and glycerophosphate oxidation in glyceraldehyde phosphate – an intermediate metabolite of glycolysis), the mechanism of conversion of fatty acids into carbohydrates in the human organism is currently being discussed. In favor of recognizing the possibility of carbohydrate synthesis of lipids states the fact that during the hibernation of animals a sharp decrease in respiratory coefficient (0.5) is observed. Such decrease in respiratory coefficient is due to the conversion of lipids into carbohydrates, which is accompanied by absorption of oxygen, since carbohydrates contain more oxygen than lipids.

In addition to the direct conversion of metabolites of these classes of substances in each other, there is a close energy relationship. Energy needs of the organism could be satisfied by oxidation of one class of organic substances when there is a deficiency of substances from other classes.

There are regulatory mechanisms for interconversion of proteins, lipids and carbohydrates, and energy integration. The driving force, most likely, is the energy state of cells, in particular, the ratio of AMP / ATP. It affects the activity of key enzymes of glycolysis, TCA cycle, fatty acid synthesis, etc.

The rate of degradation of some nutrients and biosynthesis of other is determined by physiological state and the needs of the organism for energy and metabolites.

Thus, the metabolism has a series of reactions, usually reversible, which relate the metabolism of proteins, lipids and carbohydrates in a single process.

Through the metabolism i cells n the organism function with the least expenditure of energy and substanses. This is done as a result of balanced regulatory systems of intracellular metabolism, such as intracellular, hormonal and neural regulation.