Enzyme Kinetics in Acoustically Levitated Droplets of Supercooled Water:  A Novel Approach to Cryoenzymology

The rate of the alkaline phosphatase-catalyzed hydrolysis of 4-methylumbelliferone phosphate was measured in acoustically levitated droplets of aqueous tris (50 mM) at pH 8.5 at 22 ± 2 °C and in supercooled solution at −6 ± 2 °C. At 22 °C, the rate of product formation was in excellent agreement with the rate observed in bulk solution in a cuvette, indicating that the acoustic levitation process does not alter the enzyme activity. The rate of the reaction decreased 6-fold in supercooled solution at −6 ± 2 °C. The acoustic levitator apparatus is described in detail.