Pancreatic lipase
- OMIM: 246600
- UniProt: P16233
- CAS Number: 9001-62-1
The pancreatic lipase (lipase, PL) is one of two enzymes that cleaves the ingested fats ( triglycerides) in the small intestine of mammals. This reaction is essential for the digestion of fat; so about 80 percent of the triglycerides are already split from the diet when they reach the middle duodenum. The PL belongs to the lipases and is produced in the pancreas. For the function of the protein cofactor colipase is required.
Pancreatic lipase is also responsible for the hydrolysis of retinyl esters to retinol and fatty acids, which is a part of the vitamin A intake is made possible through the diet (vitamin A is fed and taken directly as a provitamin or as retinol).
Pancreatic lipase is target in drug fight against excess weight. Since 1998, the PL inhibitor Orlistat is marketed with this indication.
Applications in medicine
Lipase plays a central role in enzyme replacement therapy in patients with impaired function of the pancreas (pancreatic insufficiency). Particularly in the case of cystic fibrosis is the gift of enzyme preparations with pancreatic powder of pork, which are normalized to a specific lipase, standard therapy. These medicines are available to protect the enzymes contained with enteric coatings. In some cases, lipase from non- animal sources is ( Rhizolipase from the mold Rhizopus oryzae, trade name: Nortase ) is used, which is characterized by a natural stability to the human stomach acid.
Laboratory diagnostics
In the laboratory diagnosis is the activity of the lipase from heparin plasma or blood serum in the clarification of upper abdominal pain, measured specifically for the diagnosis of acute pancreatitis.
Reference range for measurements at 37 ° C (color test): serum, plasma, <60 U / l
In acute pancreatitis lipase increases and is already 5 hours after onset of pain to the reference range of 60 U / l In most cases, the value of 180 U / L increases and is increased 3-6 days.
In general, the method of lipase determination is less well standardized and more prone to confounding factors as the pancreatic amylase. Therefore, it is determined in suspected acute pancreatitis, especially the pancreatic amylase. The lipase as a supplement is useful if, for technical reasons, only the total amylase can be measured or if the patient was treated with plasma expanders ( hydroxyethyl starch or dextran 70).
The lipase is glomerular filtration in the kidney, but then not excreted but reabsorbed and degraded. Therefore it does not appear in the urine, but increased nevertheless with renal insufficiency.
In endoscopic examination of the pancreas ( = ERCP Endoscopic retrograde cholangiopancreatography ) lipase increases immediately reached after six hours values of up to 720 U / l, and remains up to 3 days from the reference region of 60 U / l
Another cause for the increase in lipase without clinical significance may be the Gullo 's syndrome.
Reaction mechanism
The lipase has in its active site a catalytic triad of amino acids aspartic acid, histidine and serine. The aspartic acid deprives the histidine proton and enabled this so. The catalytically active histidine moves from serine turn a proton from, so that the nucleophilicity of the serine residue increases. This can now attack at the carbonyl carbon of an ester substrate, which is already localized in the active site. It forms a tetrahedral intermediate, from which an acyl-enzyme complex is formed. By deacetylation in a hydrolysis product of fatty acid and the original enzyme is free.