In microbiology, a biochemical pathway that consists of both catabolic and anabolic components is defined as an amphibolic pathway. A term devised by B. Davis in the year 1961, the amphibolic pathway could be effectively described by Krebs’ cycle.
The process by which glucose is biochemically broken down to produce energy, is generally referred to as cellular respiration. The most common carbohydrate for the production of energy is glucose. Fats and proteins are also used for the production of energy.
However, since these substrates cannot be converted directly into energy, they are often transformed into simpler forms. Glycerol and other fatty acids are formed by fats that are metabolized on lysis. Acetyl CoA is formed from fatty acids, while glycerol is converted into 3-phosphoglyceraldehyde (PGAL), which then passes into the respiratory pathway. The enzyme known as proteases breaks down proteins into amino acids. Depending on the type of amino acid, either pyruvate or acetyl-CoA will be formed or the Krebs cycle will be followed and respiration will be completed.
Amphibolic Pathway
Respiration refers to a reduction of complex molecules into simpler compounds in order to make an energy molecule – ATP. Thus, this pathway is called the catabolic pathway. In reality, respiration is a combination of breaking and making.
Acetyl CoA is formed when fatty acids or proteins are broken down for energy following which respiration processes take place. This process is catabolism. As and when fatty acids or proteins are required by the body, the respiratory pathway is stopped and the same acetyl-CoA compound is utilized and fatty acids are produced. Anabolism is the term used to describe this process of synthesis.
Hence, it is safe to conclude that respiration is a combination of anabolism and catabolism. Glycolysis and products of the Krebs cycle are prerequisites for the synthesis of proteins, fats, and other substances. Therefore, the respiratory pathway is also referred to as an amphibolic path.