Enolase

Enolase, also known as phosphopyruvate hydratase, is a metalloenzyme responsible for catalyzing the reversible conversion of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP) during glycolysis, the metabolic pathway that extracts energy from glucose. This reaction represents the ninth step in glycolysis and the eighth step in gluconeogenesis (the synthesis of glucose from non-carbohydrate precursors).

Enolase is present in nearly all tissues and organisms that can metabolize glucose. In eukaryotes, enolase exists as multiple isoforms, each encoded by a different gene. These isoforms can be expressed in a tissue-specific manner. For example, in mammals, there are alpha (α), beta (β), and gamma (γ) enolase isoforms. Alpha-enolase is found in most tissues, beta-enolase is specific to muscle tissue, and gamma-enolase is primarily expressed in neurons.

The enzyme functions as a dimer, and each subunit contains an active site. The mechanism of action involves two metal ions, typically magnesium (Mg²⁺), that assist in stabilizing the substrate and facilitating the removal of a proton from the 2-position of 2-PG, followed by the elimination of water to form PEP.

Beyond its glycolytic role, enolase has also been found to function as a structural protein in some organisms and to be involved in other cellular processes such as cell growth, differentiation, and inflammation. Additionally, alpha-enolase has been identified as a plasminogen receptor on the surface of various cell types, suggesting a role in fibrinolysis and tissue remodeling. In some cancers, increased enolase expression has been observed, making it a potential target for therapeutic intervention.