Enolase catalyzes the reversible dehydration of 2-phosphoglyceric acid (2-PGA) to phosphoenolpyruvate (PEP) near the end of the glycolytic pathway. During enolase catalysis, three major loops undergo a large position change upon substrate and metal ion binding, especially in the active site loop (Pro35-Ala45). The hinge sites in the active site loop are Gly residues at positions 37 and 41. To gain some information about the function of active site loop movement in catalysis and subunit interactions, the Gly residues at position 37 and 41 in yeast enolase have been mutated to Ala.  These observations confirm the active site loop movement is not only essential for correctly positioning Ser39 for coordination of the catalytic metal ion, but also plays some crucial function in maintaining the proper linkage with other loops. In turn, these precise loop conformations are essential in maintaining the correct active site structure and proper subunit interactions