LDH ,LACTATE DEHYDROGENASE

1. #1.What is LDH.    

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LDH, IS A MEMBRANE BOUND RESPIRATORY ENZYME THAT'S PLAY AN IMPORTANT ROLE IN CELLULAR RESPIRATION. It exists in five isoenzyme forms viz.LDH1 to LDH5 distributed in different body tissues. Though, these isoenzyme differ in their amino acid sequences,and found extensively in all body tissues, they catalyze the same chemical reaction.LDH levels are usually very low in the blood stream and shows a sharp increase only when an episode of tissue damage occurs. Hence, it is used extensively as a marker to determine tissue damage and in some infections such as meningitis and cancer.

#2.ROLE OF LDH 

LDH; play an important role in glycolysis.During glycolysis there is conversion of glucose to pyruvate which further gets oxidized in citric acid cycle and electron transport cycle, to release large amount of ATP.which is utilized by the cell as a source of energy.if the cell lacks the ability to oxidize pyruvate due to insufficient oxygen or any problem in citric acid cycle. then the only alternative pathway for synthesis of ATP is the glycolytic pathway.Glycolytic pathway requires sufficient glucose along with ADP.inorganic phosphate and adenosine diphosphate,and nicotinamide adenine dinucleotide for synthesizing sufficient ATP.Glucose can be easily obtained from diet or any other stored forms,and ADP and inorganic phosphate can be obtained by hydrolysis of ATP.NAD is the only limiting factor in this cycle and hence LDH plays a significant role in converting NADH produced in glycolytic pathway back to NAD to continue the glycolytic pathway.

Whenever we exercise the need for energy increases and supply of oxygen in the skeletal muscles gets reduced. This leads to an increase in LDH level, which as described above plays an important role in glycolytic pathway. Hence, in cases of muscular fatigue, high levels of LDH are seen.

#3.PULMONARY DISEASE

High levels of serum LDH; are also indicative of pulmonary disease caused by cell damage or cell death like emphysema, pneumothorax and pulmonary disease. Bronchi pneumonia and inflammatory conditions like tuberculosis also show elevated LDH levels.

 #4.cancerous cells

High levels of LDH have also been detected in cancerous cells. The C -myc gene ( responsible for cell growth and apoptosis) is found linked to LDH A gene which increases the levels of LDH in cancer cells. As it is known that cancerous cells depend on anaerobic respiration for cell growth and metabolism, this is fuelled by the A form of LDH enzyme,and hence its levels are high in cancer. Thus LDH acts as a general marker to determine the prognosis of cancer cells.

#5.MENINGITIS

Elevated levels of  LDH were seen in cerebrospinal fluid of patients suffering from meningitis. High levels of LDH 3 are seen in cases of aseptic meningitis, while high levels of LDH 4 and LDH 5 are seen in bacterial meningitis (inflammation in the protective sheath of brain and spinal cord).

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