Action of urea on human alkaline phosphatases: with a description of some automated techniques for the study of enzyme kinetics

An automated method is described for the study of enzyme kinetics. It employs a controlled substrate concentration gradient so that reaction velocities can be studied at a large number of substrate concentrations. Urea has two effects on human alkaline phosphatases: a reversible instantaneous inhibition and an irreversible time-dependent inactivation. The reversible inhibition is of the noncompetitive type. Alkaline phosphatases from different tissues show different susceptibilities to irreversible inactivation by urea. The placental enzyme is the most resistant, while bone enzyme is the most sensitive of the alkaline phosphatases examined. The alkaline phosphatases in human sera resemble those of the presumptive tissues of origin in their susceptibility to the actions of urea.