Background: Prestin converts electrical energy into mechanical work. Results: The V499G/Y501H mutation significantly impairs fast motor kinetics of prestin. Conclusion: Impaired kinetics is attributable to mutation at the Val-499 site that is conserved among SLC26 proteins regardless of their function as motors or transporters. Significance: V499G/Y501H mutated prestin provides clues to the molecular mechanisms underlying somatic electromotility and thus cochlear amplification.