Lipolysis

Lipolysis (English lipolysis, from Greek lipos, fat and lysis, dissolution ) is the hydrolytic cleavage of saponifiable lipids, ie triglycerides ( fats) and cholesterol esters by enzymes from the group of lipases. The degradation arise - in addition to mono-and diglycerides as intermediates - free fatty acids, which are released into the blood, as well as one of the alcohols glycerol or cholesterol. Lipolysis occurs in animal organisms mainly in the mobilization of depot fat in the adipocytes of adipose tissue and to a small extent in fat digestion, whereby the enzyme pancreatic lipase is used. The fatty acids formed are further broken down on the so-called β - oxidation to generate energy. The process of lipolysis is reversible; Organisms in the lipogenesis from carbohydrates such as glucose and fatty acids from fats synthesized.

Localization

About 15% of the ester bonds recorded triacylglycerides are cleaved in the stomach, the main part of the intestine, but which mainly arise monoacylglycerides and fatty acids. The remaining monoester overlap with longer chain fatty acids into micelles together, which passively diffuse through the cell membranes in the intestinal mucosa ( mucosa ). Here, the fatty acids, mono-and diacylglycerols are converted back to fats and, together with cholesterol and cholesterol esters, phospholipids and lipoproteins assembled into the chylomicrons. These represent the actual transport form of lipids; hereby recorded from the dietary lipids are mainly in the fat cells that transports the so-called adipocytes, partly also in liver and muscle tissue. The actual lipolysis runs mainly from the fat cells and is the major supplier of energy to most animals.

Stomach

In the stomach, Magenlipasen split fats to mono-and diglycerides. Although these lipases have a pH optimum of 5-7, they also work in the strongly acidic range in the stomach very effective; the proportion of the total ester cleavage, however, is low at about 15%.

Small intestine

In the small intestine, the pancreatic lipase splits the fats mainly to β - monoglycerides. Carboxylesterases and bile salt-activated lipases cleave addition to fats and cholesterol esters and β - monoglycerides completely to fatty acids and the respective alcohol.

Adipocytes

The fatty tissue is the body's fat depot for energy delivery dar. Here triglycerides are broken down into glycerol and fatty acids on demand via a lipolytic cascade. It is the rate limiting enzyme adipocyte triglyceride lipase ( ATGL ). This splits the first triglyceride from the first fatty acid. The diglyceride formed is cleaved in the second step of the hormone-sensitive lipase ( HSL), which in turn is a fatty acid, but this time is released with the formation of a monoglyceride. In the last step, the monoglyceride lipase ( MGL ) splits the monoglyceride and sets the last fatty acid and glycerin free. The are also present in adipose tissue cholesterol and retinyl esters are also degraded by the HSL with the release of fatty acids.

Activation and inhibition

Controlling the lipolysis is closely related to regulation of the blood glucose level together the one hand, increased by glucagon in fat removal, but is inhibited by insulin. The release of adrenaline, noradrenaline and cortisol, as well as other phenylalkylamines activated lipolysis. Many drugs also with so-called sympathomimetic effect, ie stimulating effect on the vegetative nervous system, act on fat loss, the effect is opposite in the two different groups of sympathomimetics. Prostaglandins, nicotinic acid and beta-blockers inhibit lipolysis.

• Adrenaline
• Noradrenaline
• Glucagon
• Adrenocorticotropic hormone (ACTH )
• Cortisol
• Thyrotropin
• Somatotropin
• Medication from the groups of alpha receptor blockers, β -agonists

• Insulin
• Prostaglandin E1
• Nicotinic acid
• Medication from the groups of beta-blockers, α -agonists

Lipolysis in food

In many foods such as milk and dairy products, oilseeds, cereals, fruits and vegetables both lipids, and they degrading enzymes are present. Here too, therefore, a lipolysis proceeds, which is undesirable in most food products. In cheese and dry sausage production, these processes are partially desirable. It formed in addition mono -and diesters of glycerol also short and medium chain fatty acids which may adversely affect taste and smell of food, such as foul-smelling butyric acid. This reduction is referred to as fat degradation, with the resulting fatty acids can also be oxidized to lipid peroxides on contact with air. Food is heated, the lipases are structurally altered by denaturation and thus inactivated. This process uses it to make about preserving milk ( " UHT ").