Glycolytic enzyme that catalyzes the conversion of 2-phosphoglycerate to phosphoenolpyruvate. Appears to have a function in striated muscle development and regeneration. (2R)-2-phosphoglycerate = H2O + phosphoenolpyruvate Mg(2+) is required for catalysis and for stabilizing the dimer. Carbohydrate degradation; glycolysis; pyruvate from D-glyceraldehyde 3-phosphate: step 4/5. Mammalian enolase is composed of 3 isozyme subunits, alpha, beta and gamma, which can form homodimers or heterodimers which are cell-type and development-specific. In vitro, interacts with several glycolytic enzymes including PKM, PGM, CKM and ALDO. Also binds PLG and troponin, in vitro. Interacts with PNKD (By similarity). Localized to the Z line. Some colocalization with CKM at M-band (By similarity). Brain (at protein level). The alpha/alpha homodimer is expressed in embryo and in most adult tissues. The alpha/beta heterodimer and the beta/beta homodimer are found in striated muscle, and the alpha/gamma heterodimer and the gamma/gamma homodimer in neurons. In striated muscle, the fiber-type order of ENO3 expression is IIB > IIX > IIA > I. During ontogenesis, there is a transition from the alpha/alpha homodimer to the alpha/beta heterodimer in striated muscle cells, and to the alpha/gamma heterodimer in nerve cells. In hindleg muscle, first expressed at 15 dpc after which, levels increase sharply between 15 dpc and 17 dpc. A steep prenatal rise in expression accompanies the formation of secondary myofibers and the development of innervation. High levels continue throughout newborn and adult stages. Beginning at postnatal day 5, a second sharp increase in expression correlates with the definitive specialization of the myofibers. Later in development, mainly expressed in fast-twitch fibers. In cardiac muscle, first expressed in the embryo in the cardiac tube. Levels decrease in degenerating myofibers, and increase with their regeneration. Belongs to the enolase family.