Lactate dehydrogenase

1i10

Reaction catalyzed by lactate dehydrogenase

Lactate dehydrogenase mechanism

Lactate dehydrogenase M4 (muscle) 1I10

Lactate Dehydrogenase B

Lactate Dehydrogenase C

Lactate dehydrogenase (LDH) is an enzyme involved in the process of glycolysis, playing a pivotal role in the metabolism of glucose to produce energy for the cell. LDH catalyzes the conversion of lactate to pyruvate and vice versa, depending on the cell's metabolic needs and oxygen availability. This enzyme is widely distributed across various tissues in the body, including the heart, liver, muscles, and kidneys, reflecting its essential role in cellular metabolism.

Structure

Lactate dehydrogenase is a tetrameric enzyme, meaning it consists of four subunit proteins. These subunits can be of two types, M (muscle) and H (heart), which combine in different proportions to form five isoenzymes of LDH: LDH-1 through LDH-5. The distribution of these isoenzymes varies among different tissues, which is clinically significant in diagnosing tissue damage and disease.

Function

The primary function of LDH is to catalyze the reversible conversion of lactate to pyruvate. This reaction is crucial in anaerobic respiration, allowing cells to continue producing energy when oxygen levels are low. In anaerobic conditions, pyruvate is reduced to lactate, and NAD+ is regenerated, enabling glycolysis to continue. Conversely, in the presence of oxygen, lactate can be converted back to pyruvate, which then enters the citric acid cycle for aerobic energy production.

Clinical Significance

Elevated levels of LDH in the blood can indicate tissue damage or disease, as cells release LDH into the bloodstream when they are damaged. Therefore, LDH is often measured as part of a diagnostic evaluation for various conditions, including heart attack, hemolytic anemia, and certain types of cancer. The specific isoenzyme patterns can help pinpoint the location and extent of tissue damage.

Isoenzymes

The five isoenzymes of LDH have distinct tissue distributions and diagnostic implications:

• LDH-1 is primarily found in the heart and red blood cells.
• LDH-2 is more concentrated in the serum.
• LDH-3 is predominantly seen in the lungs.
• LDH-4 is found in the kidneys, placenta, and pancreas.
• LDH-5 is most abundant in the liver and skeletal muscle.

The ratio of these isoenzymes in the blood can provide valuable information about the underlying cause of tissue damage.

Measurement

LDH levels are measured using a blood test, which can be ordered if a patient presents symptoms suggesting tissue damage or disease affecting organs such as the heart, liver, or lungs. The test results need to be interpreted in the context of other clinical findings and the patient's overall health status.