Anaplerotic reaction

Anaplerotic reactions are a series of biochemical reactions that replenish the tricarboxylic acid cycle (TCA cycle) with intermediates that have been depleted. These reactions are crucial for the proper functioning of the TCA cycle, which is a central component of cellular metabolism.

Overview

The term "anaplerotic" is derived from the Greek words "ana", meaning "up" or "back", and "pleroo", meaning "to fill". Thus, anaplerotic reactions are those that fill up the TCA cycle when its intermediates are used up for other metabolic processes. These reactions are particularly important in tissues with high metabolic activity, such as the liver, heart, and muscles.

Types of Anaplerotic Reactions

There are several types of anaplerotic reactions, each of which replenishes a different intermediate of the TCA cycle. These include:

• Pyruvate carboxylase reaction: This reaction converts pyruvate into oxaloacetate, replenishing this TCA cycle intermediate. This reaction is particularly important in the liver and kidneys.

• Propionyl-CoA carboxylase reaction: This reaction converts propionyl-CoA into methylmalonyl-CoA, which is then converted into succinyl-CoA, another TCA cycle intermediate. This reaction is important in the metabolism of certain amino acids and fatty acids.

• Phosphoenolpyruvate carboxykinase (PEPCK) reaction: This reaction converts oxaloacetate into phosphoenolpyruvate, which can then be converted into pyruvate, replenishing this TCA cycle intermediate. This reaction is important in gluconeogenesis.

Clinical Significance

Defects in anaplerotic reactions can lead to a variety of metabolic disorders. For example, deficiencies in pyruvate carboxylase can lead to lactic acidosis, a condition characterized by an excess of lactic acid in the body. Similarly, defects in propionyl-CoA carboxylase can lead to propionic acidemia, a condition characterized by an accumulation of propionic acid in the body.

See Also

• Tricarboxylic acid cycle
• Metabolism
• Biochemical reactions