Cytosolic enolase catalyzes the reversible reaction of 2 phosphoglycerate to form phosphoenolpyruvate and water, elevating the transfer potential of the phosphoryl group.
Enolase is a homodimer and requires Mg++ for activity. Three isozymes have been purified and biochemically characterized. The alpha isoform is expressed in many normal human tissues (Giallongo et al. 1986). The beta isoform is expressed in muscle. Evidence for its function in vivo in humans comes from studies of a patient in whom a point mutation in the gene encoding the enzyme was associated specifically with reduced enolase activity in muscle extracts and with other symptoms consistent with a defect in glycolysis (Comi et al. 2001). The gamma isoform of human enolase is normally expressed in neural tissue and is of possible clinical interest as a marker of some types of neuroendocrine and lung tumors (McAleese et al. 1988). Biochemical studies of the homologous rat proteins indicate that both homo- and heterodimers of enolase form and are enzymatically active (Rider and Taylor 1974).