Aspartate aminotransferase
| Cytoplasmic aspartate aminotransferase | ||
|---|---|---|
|
||
| Ribbon model of the dimer from wild boar ( Sus scrofa ) according to PDB 1AJS . Pyridoxal phosphate molecules (one bound to methyl aspartate) are shown as domes. | ||
| Properties of human protein | ||
| Mass / length primary structure | 412 amino acids | |
| Secondary to quaternary structure | Homodimer | |
| Cofactor | Pyridoxal phosphate | |
| Identifier | ||
| Gene name | GOT1 | |
| External IDs | ||
| Enzyme classification | ||
| EC, category | 2.6.1.1 , aminotransferase | |
| Response type | Transamination | |
| Substrate | L-aspartate + α-ketoglutarate | |
| Products | Oxaloacetate + L-glutamate | |
| Occurrence | ||
| Homology family | ASAT | |
| Parent taxon | Creature | |
Aspartate aminotransferase (ASAT, AST) , formerly serum glutamate oxaloacetate transaminase (SGOT) or glutamate oxaloacetate transaminase (GOT) , are enzymes that catalyze the conversion of α-ketoglutarate into the amino acid glutamic acid . Without this reaction step, the malate-aspartate shuttle and thus the utilization of carbohydrates in the metabolism of eukaryotes would be impossible. In addition, the mentioned reaction is part of the breakdown of several amino acids, which is why the ASAT is found in all living things.
With the development of the eukaryotes, a second isoform of ASAT became available. A distinction is made between cytoplasmic and mitochondrial ASAT (c-ASAT, m-ASAT), with the corresponding genes GOT1 and GOT2 . Plants have another form in the chloroplasts . Humans produce ASAT mainly in the skeletal muscles , heart muscles and liver . The ratio of c-ASAT / m-ASAT in the blood serum indicates the condition of the heart and liver.
Catalyzed reaction
The aspartate aminotransferase generally catalyzes the transfer of the L -amino group of an amino acid to an α-keto acid . This occurs, for example, for the reaction L - aspartate ( 1 , see also the diagram below) + α-ketoglutarate ( 2 ) ⇔ oxaloacetate ( 3 ) + L - glutamate ( 4 ). For its function, ASAT requires pyridoxal phosphate (PLP, see also vitamin B6 ), which is bound to the enzyme as a prosthetic group .
| Mitochondrial aspartate aminotransferase | ||
|---|---|---|
| Properties of human protein | ||
| Mass / length primary structure | 401 amino acids | |
| Secondary to quaternary structure | Homodimer | |
| Cofactor | Pyridoxal phosphate | |
| Identifier | ||
| Gene name | GOT2 | |
| External IDs | ||
Laboratory diagnostics
In laboratory diagnostics, the activity of the ASAT is determined from the plasma or serum in order to clarify whether a liver or biliary tract disease is present. The reference range for measurements at 37 ° C according to IFCC is <52 U / l. (Units per liter)
Elevated ASAT levels in the blood are usually the result of a liver or skeletal muscle disease or a heart attack. If the ALAT rises parallel to the ASAT , this always indicates damage to liver cells (see De-Ritis quotient ). As there is also ASAT in red blood cells , increased ASAT values are found in hemolytic blood samples. This hemolysis can also occur in vitro due to incorrect storage and long transport of the blood samples. Strong increases are found in all hepatitis as well as in toxic liver damage (e.g. from fungal poisons ). During therapy with antibiotics , the ASAT values are often increased even in otherwise healthy people. After the end of therapy, the levels drop back to normal.
See also
literature
- Neumeister, Besenthal, Liebrich: Clinical guidelines for laboratory diagnostics , Munich / Jena, Urban & Fischer, 2003 ISBN 3-437-22231-7 .
- Lothar Thomas: Labor und Diagnose , Frankfurt / Main, TH-Books, 2005, ISBN 3-9805215-5-9 .
Web links
- ALT / AST on med4you.at
- on ExPASy.org
- Laborlexikon - trade journal for laboratory medicine: GOT ISSN 1860-966X
Individual evidence
- ↑ M. Panteghini: Aspartate aminotransferase isoenzymes. Clin Biochem. 23/4/ 1990 : 311-9. PMID 2225456 .
