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Lactate Dehydrogenase Definition
Lactate Dehydrogenase is an enzyme, converts the end product of glycolysis i.e., pyruvate into lactic acid and is found in all most every organism. This process utilizes one NADH that is the energy transferring molecule. As a result, it generates NAD+, which allows the glycolysis pathway to continue.
What is Lactate Dehydrogenase?
Lactate conversion is essential in hypoxic or anaerobic conditions in the cell when there is no availability of oxygen. For the production of ATP, the cell is dependent on the glycolysis pathway only in less availability of oxygen.
This pathway requires the continual input of NAD+ to generate ATP. Lactate Dehydrogenase enzyme catalysis fermentation reaction leading to the formation of lactic acid that is responsible for the burning or muscle cramps in muscle cells during intensive exercising. The most important product of this pathway is electron carriers NAD+.
Lactate Dehydrogenase enzyme is found in all cells of the human body where it works to maintain homeostasis when hypoxic conditions occur. In the process of exercising the oxygen level within the muscles is depleted. Without the presence of oxygen that functions as the final electron acceptor in ETC, ATP synthesis drops.
For the muscle cells to work ATP is required for this they become dependent on glycolysis in absence of oxygen. But glycolysis pathway requires the supply of electron carriers to function and produce ATP.
Lactose dehydrogenase enzyme catalysis is the removal of electrons from NADH to produce NAD+ that is employed in the glycolysis pathway. ATP production is less in this pathway when compared to ETC, but it helps the cells to work and generate energy even in absence of oxygen.
Lactate Dehydrogenase Function
i. Producing Energy Without Oxygen
While the process of oxidative phosphorylation in the mitochondria produces the most energy, some energy is produced by the breakdown of glucose into pyruvate. This process, glycolysis, requires NAD+ but produces ATP. The cell can use this small amount of ATP to keep the cell operating until oxygen returns.
Instead of using the pyruvate in the Krebs cycle, the pyruvate is converted to lactic acid via lactate dehydrogenase. This process regenerates NAD+, which is needed to continue glycolysis. Continuing glycolysis produces a small amount of ATP, which allows the cell to survive.
ii. Converting Lactic Acid into Energy
When the level of oxygen is back to normal, the enzymatic function of this enzyme is reversed. That will lead to the production of pyruvate that can then move to mitochondria and be broken down releasing a large amount of ATP.
Even simple exercises may cause a lack of oxygen in some tissues, but the presence of lactate dehydrogenase ensures the supply of ATP. But this causes increased concentration of lactic acid in muscles that can cause the burn that some experience. When oxygen again rushes to these tissues, this sensation will subside.
Lactate Dehydrogenase Test
As lactate dehydrogenase only acts in absence of oxygen it can be employed to analyze tissue damage and its extent. For example, people who recently had a heart attack will have high quantities of this enzyme in their blood that has been released from damaged tissues like heart tissue in this case.
By testing the enzyme form, they can determine the type of enzyme as different tissues produce a different type of this enzyme. If the enzyme is LDH-1, it indicates that the enzyme is from heart tissue. Depending on its level in spinal and blood fluid, the intensity of damage can be ascertained and the period of the trauma can also be determined.
It can also serve as a diagnostic tool for other kinds of diseases like monitoring internal tissue damage, certain cancer treatment evaluation, and monitor conditions. It can be utilized with other kinds of tests to analyze the damage better. The most significant indicator is the level of LDH in blood and its type.
Lactate Dehydrogenase Level in Human Population
Newborn babies have a high level of LDH in their blood, which measures up to 450 units per liter. This level decreases as children age, in the case of infants it is 250 U/L, while in the case of children it declines to 170 U/L.
In a normal healthy adult, the level of this enzyme is 200 U/L. A level higher than this indicates tissue damage. The spinal fluid has a level of 40-70 U/L of LDH, a rise beyond this level indicates bacterial infections.
The treatment of cancers can be monitored by the amount of LDH in the blood. This can help the doctors understand if therapies like chemotherapy are working on the correct tissue.
This test can also be employed for anemia, meningitis, encephalitis, pre-eclampsia, HIV, identify hypothyroidism and liver disease. The presence of isoforms of LDH makes it an excellent diagnostic measure as the tissue damaged can be identified.
Lactate Dehydrogenase Isoforms
This enzyme comprises 4 hetero-subunits that work as a unit. These 4 subunits are encoded by different genes and have different structures. Five different isoforms can be observed in the case of humans that are primarily located in different tissues.
Due to these isoforms, it is easy to identify the tissue that produced this enzyme. For example, LDH-1 isoform is found in tissues of the brain, blood cells, and the heart. While LDH-3 form is seen in the case of lungs.
Commercial Uses of Lactate Dehydrogenase
It is also a commercial enzyme that is utilized to create many dairy products like kefir, yogurt, and cottage cheese. It is the enzyme responsible for making milk sour. It is employed by wineries and brewers to give a characteristic sour taste to their wine or beer. This sour taste is attributed to the production of lactose.
Lactate Dehydrogenase Citations
- Elevated lactate dehydrogenase (LDH) can be a marker of immune suppression in cancer: Interplay between hematologic and solid neoplastic clones and their microenvironments. Cancer Biomark . 2017 Jul 4;19(4):353-363.
- Lactate Dehydrogenase Inhibition: Biochemical Relevance and Therapeutical Potential. Curr Med Chem . 2019;26(18):3242-3252.
- Lactate dehydrogenase A: A key player in carcinogenesis and potential target in cancer therapy. Cancer Med . 2018 Dec;7(12):6124-6136.
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