properties of matter : From Bovine Erythrocytes. Useful in carboxy group transfers and reduction reactions. Supplied as a dialyzed, lyophilized powder. Unit Definition:One unit is determined by the electrometric method of Wilbur and Anderson (J. Bio. Chem., 176,147 (1948)), in which the time required (in seconds) for a saturated CO2 solution to lower the pH of 0.02M Tris-HCl buffer from 8.3 to 6.3, at 0°C is determined.