Lactate dehydrogenase

  • CAS Number: 9001-60-9

L- lactate dehydrogenase (LDH ) is an enzyme that catalyzes the formation of L- lactate and NAD and NADH from the pyruvate. The reaction is reversible. LDH is used in all cells from almost all living things. It is a component of the lactic acid fermentation. In higher animals, is secreted by cells LDH accumulates due to great stability also in hemolymph and blood. There it can be used as a laboratory parameter indicating cell damage. The very similar D -lactate dehydrogenase is found only in the lower animals, microorganisms and plants.

Biochemistry

The reduction of pyruvate to lactate by LDH and the cofactor NADH has feature of the lactic acid fermentation, is recovered in the energy from glucose with no oxygen consumption. Lactate formation fulfills the purpose of regenerating NAD , which is needed in the glycolysis of GAPDH. Lactate itself is in the fermentation process does not continue to be used and is excreted by the cell as the final product. In humans and higher animals, lactate is transported via the blood stream to the liver. There takes place in the presence of NAD , the reverse reaction of the LDH. Lactate is oxidized to pyruvate and is the metabolism thus accessible again. The reaction proceeds in some muscle tissue, if NAD is available.

The reduction of pyruvate to lactate is highly exergonic ( ΔG0 '= -25 kJ / mol).

Isoforms

In the human body is found five isoenzymes of LDH, the HBDH a summary of LDH -1 and LDH -2 corresponds. Each of these enzymes is composed of four subunits. There are a total of two types of subunits, the H and M- shape, depending on the nature of the composition of these two types, five possible combinations are; indicated are the predominant isoenzymes in each organ:

  • LDH -1 ( 4H) - in the heart
  • LDH -2 ( 3H1M ) - in the lymphatic system
  • LDH -3 ( 2H2M ) - in the cells of the lung
  • LDH -4 ( 1H3M ) - in various organs
  • LDH -5 ( 4M ) - within the liver and striated muscle

It should be noted that happen, other LDH isoenzymes in these organs, so is the heart and LDH -2 ( and LDH -3 tracks) to find; LDH -1 is the prevalent form.

Laboratory diagnostics

The lactate dehydrogenase ( LDH) is used as a diagnostic parameter to detect increased damage to cells. Lysing cells release the enzyme free. Due to high stability LDH remains in the extracellular space and accumulates in pathological cell damage in the blood. Therein, or in plasma / serum LDH activity is measured. Under physiological conditions, the activity of the LDH of serum is up to 240 U / l Rises above this value, this is due to a decomposition of cells. It is then based on the determination of LDH isoenzymes also understand what organ is due to the origin of the enzyme increase. Within the blood serum can be all isoforms of LDH detected, and LDH -1 and -2 predominate. An increase of LDH -1 LDH -2 may indicate an increased cell death of myocardial cells or blood cells, on the other hand, an increase in the LDH -5 suggest that the liver injury. Ultimately, a diagnosis can only be made in conjunction of several findings.

Especially with hematological diseases, muscle diseases and in liver and biliary tract disease may be about a laboratory diagnostic LDH assay information on which damages have occurred. Previously, the LDH activity was also determined in heart muscle diseases, which today thanks to recent measurements ( Cardiac troponin ), although is not necessary anymore, but is still carried out in some cases, especially when it comes to the detection of a no longer fresh myocardial infarction. Compared to other heart muscle-specific enzymes or enzyme combinations remain LDH -1 and LDH -2 is relatively long detectable. Occurred cell damage can be detected even after up to 20 days.

Reference range

Reference range for measurements at 37 ° C according to IFCC

  • Every: < 245 U / l

Interpretation

Since the LDH is present in all tissues, with elevated levels of only the first statement can be made that tissue damage has taken place. Most commonly, these occur in connection with diseases of the liver, heart, skeletal muscles, the lung or the blood ( anemia, hemolysis or mononucleosis ).

Causes

LDH is in red blood cells (erythrocytes) in large quantity available. Why have u.U. hemolytic blood samples false positive on test results, as these can also be caused hemolysis in vitro by improper storage, improper acceptance or long transport of samples.

Importance in research

In the life sciences and pharmacology extracellular LDH is used as a marker for cell damage which may occur, for example in toxicological studies. Law LDH released into the medium can be demonstrated among other things by their reaction with tetrazolium salts to formazan dyes.

CAS registry number Glyceraldehyde 3-phosphate dehydrogenase Isozyme Tissue (biology) Tetrazolium chloride
379569
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